I'm an on-ear open junkie, so this high praise says a lot about the PX95.  A list of on-ear opens I have in various drawers:  AKG K403, PX100-ii, PortaPros, Jays V-Jays, SR-80 and some more that I can't remember right now.  My current favourite is the PX95.
 
Finally, an on-ear open that actually has decent bass extension without the PortaPro's boominess.  There's no Sennheiser "veil" or "mid-bass hump" here (wow!), so this is closer to the PortaPros than the PX100s.  Mids are decent - few on-ear opens screw those up, but what you trade in for your $40 is some detail in the very highs.  Soundstage is very good, which is normal for an on-ear open.
 
However, the biggest shock and delight from my PX95 ownership has been its ultra light weight.  I think these are the lightest on-ear open headphones I've ever used and it is so easy to just leave them on all day and night.  Will these replace my workhorse K403s at my 9+hr/day desk?  Quite possibly... but I'd be paranoid of having them stolen though.
 
vs. the PX100-ii... the PX100 comes with a carry case and folds really nicely for travel.  The PX95 can't travel.  PX100 may have a bit more detail in the highs.
vs. the PortaPro... PX95 is way more comfortable and easy to put on.  Headband does not try to pull my hair out and it isn't a pain to adjust.  As stated before, Porta's boominess gets annoying and extended wear creates some pressure points if not perfectly adjusted.
vs. the V-Jays... the V-Jays do sound better sometimes, but L and R are clearly marked on the PX95.. the VJays make it difficult to tell L and R.. and that annoys me.
vs. the K403... tough call, still evaluating this one.  The K403 is a bit lighter on bass while still having great extension while still having great highs, making it better for doing work.  The K403 folds flat for desk drawer storage...
vs. the SR-80.  I can't compare.  The SR-80 has better sound in almost all respects, but weighs a TON and the cable is far to large and heavy for portable use.
 
If you see the PX95 for less than $35 and you love on-ear open headphones.  Click buy, don't hesitate, just click buy!!!

General Review
Unfortunately not the be-all-end-all.
After seeing and hearing the MM450X at the Frankfurt Airport I though it had it all and could do it all: Bluetooth apt-x, noise cancelling, bluetooth headset, wired passive, talk-through, compact and foldable, easy to recharge, and with decent sound.
After some ownership i've found that it's a bit of a compromise and the perfect do-it-all is still yet to be made.
 
Features: Gadget-wise the MM 450-x has it all and performs. Apt-x is noticeably better than standard aac A2DP. Headset microphones are excellent as they noise-cancel. NoiseGard works, though not as well as the QC15, and nowhere near my Ety's, but it would be more fair to compare them with the similarly on-ear AE2. Perhaps next time I'm sitting next to someone with one i'll ask.
Talk-through is also a great feature when sitting next to coworkers or responding to FAs - pulling deep IEMs out and back in is a hassle.
The MM450 also wins in usability - buttons are easy to find and pleasant to press, and the ability to use BT without NoiseGard is useful.
Battery life is suitable - about 20hrs in wired NoiseGard mode is more than the amount of flying you'll want to do. 10hrs in BT mode is enough for a long day of work where you probably don't need NoiseGard, and 8hrs with BT and NoiseGard... I'm not sure where exactly you'd use this - on a train/bus?
 
Comfort: the MM450X disappoints a bit here. Most on-ears now have soft foam pads. The pads on these are definitely on the hard side. I'm going to try to fit soft foam pads from the K450.
 
Portability:  Not quite as compact as the AKG K450 or the Sennheiser PX100-ii but still better than carry a full-size Hp around...
 
Sound: This is the biggest let down. For something with an MSRP of the HD600 I expected better. Highs are detailed, but mids are dry and grainy. Bass is there but lost in poor fitment. I'm hoping the cushier K450 pads fix the sound.
With NoiseGard on the bass is boosted slightly, but this is in a quiet environment.

Pleasant overall. The bit of extra bass extension should please most but is not boomy.  Strong details and depth which might even be a bit harsh in the treble.  Great for orchestral.
 
Worn over the ear only so no microphonics.  tri-flanges isolate well, but can be generally difficult to insert and uncomfortable due to the wide nozzle.  Memory wire could be annoying.  Everything should come with a case like this.  Not a huge fan of clear, but secret service wanna-bes might.

Detailed highs are slightly noisy, no soundstage at all,  thumpy, boomy bass can be annoying and mids are weaker.  Definite V profile w/ sibilance.  Excellent for Sci Fi movies!
Minimal microphonics - none when worn over.  Great accessories - bi-flange works great and metal body is a nice quality touch.  Can be a little hard to remove.  Covering the rear ports fixes the boomy bass which making the mids/highs muddier.  Basically a sonic disaster.

Very nicely balanced overall. Bass very slightly lacking, but this is a matter of taste.  Lots of tips to choose from, and came with foamies!
 
Cheaply put together though.  Loads of microphonics.  Clip is useless.  Thought I heard some imbalance but it went away with burn-in.  Questionable quality?
 
After further burn-in, my Betas became very bass dominant, though still with excellent overall sound quality.  I wouldn't buy the Betas again.  Sent back to Hong Kong for warranty and I sold the replacements.

Just generally good and hard to find fault with.  Not really deep low bass, but enough to be pleasant.  Mid-bass has good presence and there is excellent clarity and detail in mids and highs. I found soundstage to be a little congested and overall a bit of a "thin" sound.  While many people have praised these, I find them a little boring to listen to.  The highs do not have an audiophile-grade "zing".  Clamp force a bit high at first and ear pads could be more comfortable.  A little more closed than semi-open so soundstage is not that wide.

While sound is excellent I'm not a fan of knock offs and these are knock offs of AKGs and ATs.  If they had their own style I would buy more Superlux products, but their entire lineup seems to "borrow" design cues from others.  It's too bad, because sonically they're excellent though after some time of listening I did not enjoy the highs as much.  That tells me it's easier than we think to make good sound, but coming up with a great looking headphone - that's worth paying extra for.

Awkward fitment, but pleasant sound.  Good control of microphonics, even without wearing cord up (only really one way to wear it).  R Ch lost trebel after 10hrs of burn in!
 
2nd pair.  These don't isolate that well, but super wide soundstage, great detail, and suitable amount of bass that extends well into the deep.  Very fun to listen to.

THese are definitely mid centric, maybe even bordering on bright.  Bass, as said before is there, even with a good seal, maintains its backstage presence.  Mids and treble are clear with great detail and that superwide soundstage.  Only the awkward fitment, difficult sealing, and de-emphasis of bass take away from an otherwise great experience.
 

Got these as a gift, sold them for $20 to someone who wanted noise cancelling.  I warned them that the noise cancelling wasn't very good but they still wanted them.  This will cancel an HVAC fan, or some traffic noise outside your building, but that's about it.  These aren't Quiet Comforts, nor are they IEMs.  These cancel noise like a shallow IEM with the dynamic range of a cheap ear bud.  If for some reason you really want an on-ear headphone, not IEMs or over-ear, go with a Philips model that has memory foam.  Frankly passive noise isolation is better than the active cancelling on these.  You'll save yourself AAA batteries which you will go through very quickly because you'll always accidentally hit the on switch when putting them away.
 
However, they were reasonably comfortable on the ear, and if you really, really want active noise cancelling and don't care about sound quality, then these might just be for you.  It also comes with an excellent, hard to replace airline adapter.  And since these will be next to useless on the airplane, you might as well take out the adapter and use it with some IEMs!

A long time ago it wasn't as easy to find a decent set of discount headphones and I didn't know about head-fi so I got these just to test all the stereos I was working on.  These were my first circumaural headphone so I'll always remember them for that.
 
These are somewhat big cans, but very isolating. Sub bass seems to be missing as there's no "rumble" to these.  Vocals are unclear, messy, muddy.  Rest of the range is good but very closed.  Highs could use a bit more detail, otherwise well balanced.  Mechanically these are a disaster.  The plastic headband isn't comfortable, they don't fold, make lots of noise, and there are two cords to tangle. Sweaty earpads = Not comfortable.  Long 3m cord and adapter included, making it OK for basic TV or radio listening, but nowadays thanks to head-fi there are other higher sound quality choices at this price range.  I'd recommend the Coby Deep Bass over these if your budget is that tight.