Clones of the Tascam MX2.  Build quality of the headset is strong, the metal sliders have a good grip when adjusting the size.  Quite comfortable.  2.7% of reviews mention about jack plug failures. Come in a selection of colors, white, black/red or black.
 
Sound quality.  Very flat neutral sound ideal for studio monitoring, but they are musical too, they have a nice warmth due to lower mids being slightly forward and the upper mids are non fatiguing and slightly back whilst having an airy sound.  Sub bass is very pleasant but not at basshead levels, just well balanced.  Highs are just loud enough to be pleasant and neutral.  Soundstage seems to be wide, at least as wide as my PSB M4U1.  Compared to the M4U1 they are less raspy (not as aggressive in the upper mids/lower treble).  They also lose out in terms of detail and speed but for £25 the Prodipe are amazing value.  I am now selling my PSB M4U1 as I love the warm neutral sound of my Prodipes.  In fact I actually like these the most out of the 5 headphones I own, they are very similar sounding to my Philips HP1000 open headphones with hardly any difference in the soundstage and sound tonally similar with more bass.  I would say these sound like £150 headphones, not far off from the Beyer DT250s either.

The reviewed headphones are clones of the Tascam, they are Prodipe 3000.
 
Build quality of the headset is strong, the metal sliders have a good grip when adjusting the size.  Quite comfortable.  2.7% of reviews mention about jack plug failures. Come in a selection of colors, white, black/red or black.
 
Sound quality.  Very flat neutral sound ideal for studio monitoring, but they are musical too, they have a nice warmth due to lower mids being slightly forward and the upper mids are non fatiguing and slightly back whilst sounding airy.  Sub bass is very pleasant but not at basshead levels, just well balanced.  Highs are just loud enough to be pleasant and neutral.  Soundstage seems to be wide, at least as wide as my PSB M4U1.  Compared to the M4U1 they are less raspy (not as aggressive in the upper mids/lower treble).  They also lose out in terms of detail and speed but for £25 the Prodipe are amazing value.  I am now selling my PSB M4U1 as I love the warm neutral sound of my Prodipes.  In fact I actually like these the most out of the 5 headphones I own, they are very similar sounding to my Philips HP1000 open headphones with hardly any difference in the soundstage and sound tonally similar with more bass.  I would say these sound like £150 headphones, not far off from the Beyer DT250s either.

I was looking for an alternative to my PSB M4U1 as they are a bit strident in the treble.  I won the A5 Pro on ebay for £70 and I am very pleased with them. 
 
Comfort - after 1 and a half hours the top of my head aches a bit from the lack of soft padding on the headband.  Not a problem since I would have a break.  Clamping force is very secure and is not a problem for my small to medium sized head.  The lead is just long enough at 1.4m stretching to 3m
 
Sound - There is a nice smooth and defined mid bass and slightly less sub bass, not quite as much mid bass as the open Philips X1 but cleaner sounding.  Punchiness in the mid bass is very pleasing, giving a very accurate, controlled reference.  Mids are very slightly dark and non fatiguing, bright enough for clear vocals and guitars, detailed and clean.  Treble is very natural, there is a smooth curve with good extension that is clear and yet not fatiguing, indeed the treble is far more pleasant and natural than my PSB M4U1 which is strident.  Mids are also slightly darker than the PSB, but neutral.  I have also compared the Philips with the Sony MDR-100AAP and the Philips has more detail across the board, punchier bass (not quite as much sub bass) and better imaging.  The A5 Pro handle all the genres that I like very well, be it jazz (pianos sound great), rock, pop or dance.  Newer dance music cds really show what the A5 Pro can do with punchy bass and detailed sound.  With good quality headphones you need to have good quality music as opposed to compressed mp3s to notice the difference between good headphones and cheaper ones.  Comparing the PSB M4U1 to them is that the PSB has less bass impact, harsher treble, slightly wider sound stage and more comfortable.
 
Summary - Not sure if they are worth the £300 rrp but on ebay you can get these for around £100 or less which is an absolute bargain, hi fidelity listening at a budget price.  Maybe the likes of the Bowers p7 can offer slightly wider soundstage but other than that I don't think you can get better sound quality unless you spend £400 or more.
 
UPDATE:  I got fed up of the discomfort from the headband which was not padded enough, so I sold them after having them for about 2 months.

I have the Studiospares M1000, identical to the HM5 and won them on ebay for £26 which was an absolute bargain.  The Studiospares retail brand new for £64 plus delivery.
 
They have a secure clamp pressure but are comfortable due to the thick, soft pads.  I like the secure feeling that they won't slide off the head, I think the overall clamping and comfort is near perfect for my small to medium sized head.  One of the adjuster sliders is a bit loose but does not matter due to the clamping force.
 
Sound is quite neutral except for very slightly forward mids around 1khz to 4khz, but without any spikes and very smooth transition which makes for a very pleasant sound signature, perhaps not neutral enough for mixing in a studio.  Bass and treble are mixed well with the mids although this is not a headphone for bassheads.  Treble is not excessive and very pleasing. They are as smooth sounding as the beautiful earcups look, almost as if the physical aspects have influenced the sound!
 
Soundstage is very wide for closed cans and there seems to be a slight airiness in the presentation, maybe due to the deep earcups combined with the small slotted vents.  I do not hear any echo which some people have reported, nor any boomy bass, bass is well defined.
 
These do not have the detail and accurate imaging of my Philips A5 Pro and PSB M4U1 but they are more expensive headphones.  One reviewer said that the Philips Uptown was superior to the HM5 but I did not like the slightly veiled mids and slightly boomy bass of the Uptowns. 
 
I would say that the HM5s are the best value closed cans for under £70.  If you are lucky you can get the Philips A5 Pro for under £100 on ebay although they are not as comfortable as the HM5.  I think you can get the Yamaha hph mt220 for £120 and the PSB M4U1 for £130, I have not tried the Yamaha but have heard good things about them.  The PSB have great detail and soundstage but I do not like the harsh treble.  For open headphones you can get the Yamaha hph-200 for £70 which is fantastic, also the AKG k612 is meant to be very good for £89.

I just bought these for £100 secondhand off ebay and I don't think I will get any better for the price, although I have not auditioned the AKG K612.  Bass is punchy, detailed, well textured.  Mids are very smooth, neutral, no spikes whatsoever, highs are sparkly and just right in the mix.  Overall, the detail level is great, clarity is of a high standard as you would expect and the speed response is great.  The soundstage is so airy and wide it really makes for a dreamy wonderful experience and especially with the low to mid bass response which fills the sound in beautifully.  The pads are so lush and comfortable with the velour padding, these feel as good as they sound!  Overall the X1s sound expensive and refined and they are definitely keepers.

These are underrated on headfi, I find them to have an airy wide soundstage with a warm bassy sound signature. They have a warm midrange, 70's jazz with electric piano sounds wonderful.  Treble is not that smooth but is just right in the mix, extension is good.  You cannot pin-point instruments with accuracy though due to the sound not being very detailed and focused although it is very adequate for the price paid.  I will be selling my Philips shp8500 because the Koss have a warmer midrange and airier soundstage.  I think they have a unique sound of their own due to the midrange tone.  The bass is quite punchy and was a pleasant surprise when I first heard them, although sub bass is nothing to shout about.

Bought these for just over £5 from ebay , they retail for around £13 on amazon uk.  Sound signature is very natural with smooth midrange.  Occasionally the highs can be slightly recessed but they are very clear along with clear bass and mids.  Bass level is superb and is very satisfying.  Detail is about average, but excellent considering the competition in this price range.  Soundstage is amazingly wide for such cheap closed-back headphones, although compared to my Philips shp8500's they dont have as much grace or finesse in soundstage presentation.  If you are looking for budget portable headphones, I would highly recommend these.

Bought these from ebay for £15 .  Originally I believe they were going for £50 in 2007 then reduced to £20 - £30.  Firstly what struck me was the warm sound and nicely presented bass, no problems with bass clarity here!  They are semi-open as there are tiny holes for the hinge pivoting on the earcups.  Also they feature angled drivers so you get a wide soundstage with clear instrument separation.  They are the best headphones I have had and having had quite a few (see my profile) that is saying something, although I have never really owned expensive ones apart from the Sennheiser HD598 which lacked bass in my opinion, and the Philips Fidelio X1, which had a neutral midrange.  Also, a fellow reviewer here on headfi by the name of ljokerl has praised these shp8500's and he has reviewed lots and lots of portable headphones in depth (search for 'shootout' here on headfi). The only criticism is that the treble is sometimes slightly lacking on some recordings, but most of the time it is just right. Comfort is really nice, the cloth earcups are so comfy and the headband is well padded.

Build quality
 
Very light with light to medium clamping force, soft pleather cushioning makes for very comfortable wearing for long periods.  Ratchet mechanism is strong and precise for adjusting the headband.  Earcups swivel up, down, left and right.  The lead is a generous 3 meters long. 
 
Sound quality
 
The bass is dynamic to be heard very fully when needed and also it extends quite deep.  Punchiness is average.  Mids are mellow, reproducing vocals quite flat, but not too veiled to spoil the listening experience.  Chocolate-like is another way to describe the mids!  Mids to treble onwards has a linear flat sound signature, so that cymbals are very accurately reproduced, there are no upper-mid/treble spikes at all, unlike many headphones that have an upper-mid emphasis.  Upper treble is very pleasing and sparkly.  Soundstage is very elegant and wide, for example, panned reverbs and echoes of guitars on Pink Floyd's Pulse album are quite detailed, compared to the Philips uptown.  This is due to the semi-open design compared to the uptowns closed design.  Instrument separation is very good.
 
To summarize, the Philips shp3000 have a similar sound signature to the Philips fidelio x1, especially the mids.  Perhaps you could call them 'the poor man's fidelio x1', except maybe there is not quite as much detail retrieval.  Having come from the bright sounding Philips hp890, I had to adjust to the mellow mids; Indeed, the mids are slightly less pronounced than the Philips uptown as well as the treble and bass quantity, very slightly so.  These have now replaced my Philips hp890 because the mids are less harsh and the soundstage is almost as wide.  Sound signature is just perfect when listening to Men At Work's album 'Business As Usual' or Neil Ardley's 'Harmony Of The Spheres'.  The only downside of these headphones is that not everyone might like the mellow mids - vocals and some guitars do not shine too well although it makes for a non-fatiguing listen.  That's not to say that the mids are veiled, just chocolate-like.  Amazing value at £28 from amazon uk, surely they compete with headphones costing 4 times the price!

Review of HP890's
 
Build quality
 
The luxurious blue velour pads are very comfy, along with the rubber headband, although I would say that the clamping force is slightly weak which is not so good due to the heavy weight of these headphones and they feel as if they would come off easily if I leaned down.  The joints seem to be a bit vulnerable but should be sturdy enough with good care taken. 
 
Sound
 
Good bass extension, they go low and the amount of bass is impressive considering that they are open-backed.  The bass is clear without any bloating and fast enough in sharpness.  Mids tend to be a bit recessed and have average detail, although they are clear enough to be enjoyable.  Highs are the forte, very clear and sweet, excellent pinpointing within the sound field which even surpassed my Yamaha HPH-200's in this respect.  Soundstage is very wide, sometimes sound comes very much from the left but that is because there is no right-panned instruments at that time.  Maybe this is a pitfall of the wide soundstage, but the advantage is that the instruments are very cleanly and precisely placed in the stereo field.  The drivers are nice big 50mm ones and are angled. 
 
Summary
 
Overall, I think that the HP890's could rival the AKG K701s and Sennheiser HD600's although you are probably not going to get the clarity of those, I can't say as I have not owned them, but have read that they have good soundstage and clarity.  I was lucky to have bought my HP890's new from Amazon in July 2013, a long time after these headphones were doing the rounds back in 2001/2002.  I gladly paid £79 despite knowing that they were originally £50 and they are still good value.  They have good treble response along with wide soundstage although I would not recommend them for bassheads, although the bass is very impressive. 

Build quality
 
Well built for the price, the cloth ear covers can get a bit worn in places. 
 
Sound quality
 
Tight and defined bass that extends quite deep, clear, defined mids, slightly prominent lower treble, treble well extended and very clear.  Overall quite neutral in sound signature.  Soundstage is wide and airy.  These are better than the Grado sr60 beating them in soundstage and clarity, except for very slightly less bass.  Not too different to the bigger Philips hp890s, but again, not quite as much bass.  Value for money is really really good!  Paid £13 for them on ebay uk.

Build quality.
 
The earcup padding is exquisite with it's soft, smooth faux leather, as well as the beautifully padded headband.  The model I bought for £49 off Amazon was the all black one without the volume control as I had demoed the silver one with the volume control and it had a channel imbalance, so I thought that the all black version would be a safe bet.  I like the understated look, the satin finish of the earcups is very nice as well as the excellent stitching of the faux leather.
 
Sound.
 
The bass is dynamic and when called for, goes deep.  Generally the bass is above neutral but does not overshadow any of the rest of the sound signature.  Mids are quite detailed with a warm sound, highs are clear and just right in amount, sparkly enough and not veiled.  I am now selling my open-back Philips HP890 due to warmer sound and more bass of the uptowns, despite the fact that the instrument separation is slightly less defined on the uptowns due to slightly narrower soundstage.  Having said that, the soundstage on the uptowns is wide enough to be like an open backed set, possibly due to the angled drivers, definitely impressive for closed-back headphones.    I have tried many headphones and none have surpassed the sound quality of the HP890s, so these uptowns have earned the right to surpass them!  My other set of headphones is the Yamaha HPH-200 and the sound of those are more detailed and sharper but more fatiguing with allot of treble and less bass extension.  Compared to my Philips SHP5401 the uptowns have more bass and less upper midrange.  I have read that the uptowns are better than the m50s and Brainwavz HM5 and in my opinion they are underrated, like many other Philips headphones.