This is attempt number two at this comparison.  I want to repeat my setup conditions.  This comparison is done via a single, diverse song.  Each earphone will be compared against the M9.  Each earphone is EQed to (ear) flat that has previously been determined through testing.  The earphones will be run off my Meier Corda 2Move using the DAC + amp.  The end result is each earphone will be on the same level response wise from 30Hz to 16kHz, and the variations will mainly be the variation in sound signature.  The earphones used are the ones I have lying around and can compare against.  These are all decent earphones of a much higher value.  The earphones included are the Sleek Audio SA6, Denon C700, Klipsch Custom 3, and Yuin OK1.  The goal of this comparison is to highlight some capabilities and limitations of the M9 earphone and to define a relative performance level.
 
SA6 vs. M9
The SA6 is an earphone I really like.  It has an airy and very transparent sound that’s more like thinking sound than hearing sound. Few earphones offer really good transparency and direct sense that lets the earphone disappear.  Note weight of the SA6 is very good.  Some BA drivers are too clean with very short, spaced notes that lack body and texture like the PFE or SE530 which can sound weak in presence and lacking articulation.  While the SA6 doesn’t have the thick, textured note of the ER4S or Custom 3, it is a good middle ground that has a good weight and emphasis and a natural sense.  Both the SA6 and M9 are geared towards a smoother presense.  The SA6 offers more dynamic range and cleanliness of note.  The M9 offers an edgier, more direct note.  While the M9 is smoothed some, it retains good note detail and control that prevents it from coming across muddy.  While the SA6 offers more note energy, the M9 does offer a more robust low end with a greater visceral sense as well as a little more expected edge and sparkle on the top end.  The SA6 does show that the M9 could use a little more dynamic breadth and space and air in the presentation.  Mostly it’s just the shortcomings of a budget level driver.  The M9 is good enough however that it doesn’t come across lacking.
C700 vs. M9
I’ve always liked the C700.  It has a great sense of realism and a very dynamic and well articulated note.  The sound can come across slightly veiled and grainy when compared to some better earphones, but it offers a life-like sound and such effortless dynamic breadth that isn’t there in a lot of other earphones.  The C700 does suffer from a couple major faults though.  First, its bass is very loose and lacks a lot of control.  This can make the bass very floppy at higher output levels.  Second, despite being an IEM in design, it offers zero isolation.  It’s as good as an ear bud and needs to be used in a quiet room.  It’s pretty much stuck for critical listening duty.  The C700 is an outstanding example of what it means to have effortless dynamic range.  When compared against the M9, it blatantly shows the limitation of the M9 driver.  The M9 just doesn’t share the same breadth between energy and silence.  The M9 does show that it does retain a good level of detail and articulation though.  The M9 also does bass considerably better than the C700.  The M9 has the control that the C700 simply lacks, and it lets the bass be more articulate and defined.  The M9 just does bass quite well and highlights the low frequency shortcoming of the C700.
 
Custom 3 vs. M9
The Custom 3 is a largely misunderstood earphone.  It is so misunderstood that the Custom 3 is Klipsch’s best IEM, better than the X10 (their words), and they discontinued it due to poor sales.  The drivers chosen by Klipsch for this IEM are quite good and cover the spectrum well.  Klipsch gapped the x-over point a little to emphasize bass and treble, not something I personally prefer, but it can be EQed.  This is just a really good driver package.  The Custom 3 excels at some things many other earphones suffer from.  First, the drivers offer a thick, well textured note, very uncommon for a BA setup.  Second, the Custom 3 has a very good sound stage, very well sized and very linear in distancing.  While the note is thick and blended for a BA, similar to the ER4S, it retains an excellent, clean sound due to it being a BA.  It’s sort of the best of both worlds in a sense.  The Custom 3 is simply on a whole other level versus the M9.  It offers a thich, textured note, excellent dynamic range, great engery, space, and simply does a lot of things really well.  A great sound stage allows an earphone to separate and layer sounds.  Comparatively, the M9 comes across a big congested.  The M9 does offer a good sense of size, but the Custom 3 shows that there is room to gain.  Even stepping back to the M9, it does remain separated enough not to get messy.  The overall presentation retains a good sense of detail and control, enough not to muddy together the sounds which is impressive for such a budget level product.  The M9 may not offer the layering and linearity of depth, but it has a deepness to it that prevents it from sounding closed in.
 
OK1 vs. M9
The OK1 is a long time favorite of mine.  It is a bud which is a little out of the mix of IEMs here, but it’s a bud I’ve held on to for a long time even after owning and selling many high end IEMs.  The OK1 is an incredibly transparent, airy, and direct sound.  I often describe it liking dreaming sound rather than hearing sound because the sound just exists.  This is a heavily dependent earphone though.  It is quite bright in stock form and takes a bit of EQing to flatten out.  It requires a robust amp to feed enough wattage to support effortless operation at moderate output.  It’s a product I wouldn’t readily recommend without capable EQing and a powerful amp to support it.  Yet if you do provide the necessary hardware, it is an exceptional product and offers some of the most direct and life-like sound.  It’s aggressive, direct, and conveys a great sense of emotion in the music.  There is a lot of linearity with the presentation and sound stage.  The OK1 offers a lot of air and sparkle to the notes and against the M9, it does show how much more there could be.  It is nice that the M9 is open enough and with enough edge to not really come across too lacking.  It is immediately apparent there should be more, but at the same time you don’t feel lacking.  The OK1 offers a very aggressive note with a high level of sharpness and impact.  Despite being a treble geared earbud, bass is surprisingly robust and energetic and does outpace the M9 in this regard.  The M9 does offer a greater weight though, and you get more reverburation.  I’m always drawn back to how good the bass is on the M9.  It’s not as articulate or detailed as, say, the IE8, but it offers great extension and control and defines a range of frequencies very well.
 
So where does this place the M9?  Well, it could be better in a lot of ways.  The budget meeting driver really does limit it’s output capability and dynamic range.  However, the driver actually does cover the frequency spectrum really well.  Bass is surprisingly good and surprisingly well controlled.  Midrange and treble is well detailed and with enough bite to satisfy.  It’s a little laid back dynamically and a little smoothed together in note, but it still offers good detail and definition and enough even up top not to come cross muddy or slurred.  I am comparing it against products that are many magnitudes more expensive, and I have personally used most of the top end IEMs out there.  The M9 just ends up performing quite well and lacks a lot of the major faults many budget level products have.  Could it be better?  Sure.  Could it be better at its $30 price point?  Probably not.  Frankly, there’s a number of $60-$80 earphones I’ve used that I would less prefer than the M9.  The M9 just does enough right at a great enough price to simply be a solid buy.  Even what it does poorly it simply does well enough not to create a need to have better.

Nice comparisons
 
I think I finally found a good use for my M9. Once in a while I forget to charge my clip+ and the battery dies while I'm still on my commute which means I'm forced to use my crappy phone output which sounds really bad and worst of all has this really loud beep whenever I put any decent earphone in it. I decided to change from my e-Q7 to the M9 on my phone output and it sounds pretty good since it does not sound very good with the e-Q7 since it shows the very bad sound capabilities of my phone. I've been putting the M9 in my bag just in case and today it was needed
 

Yeah, the M9 is a decent earphone.  It doesn't need much power.  It has good detail but is smooth and laid back enough to not trouble you with a less than ideal audio device or recording.  It does enough things well to just sound good overall.  My only real complaint is mainly a side effect of the budget gearing.  The driver simply lacks the throw to get loud cleanly.  This limits its cleanliness at higher output levels.  As well, it does limit dynamic breadth to some degree.

So it sounds better at lower volume? I haven't tried it since I don't typically listen at very high volumes. I usually turn it up a bit more for dynamics but not by too much but typically for me the dynamics that I've tried have usually been not as loud as BA when on the same volume so I do have to turn it up a bit.
 
I'm just happy to have found a use for it although it won't be daily use since I usually don't run out of battery on my clip+ unless I do something like what I did today which happens once every couple weeks.

Yeah, moderate to high output is its greatest weakness.  It's simply that the driver used is only clean over its relatively small linear range.  If you push it, movement becomes less linear, and you just introduce more distortion and less control.  It just sounds messier and the sound stage breaks down too from everything muddying together.  It's great at low volumes, and that's where it should stay.  Isolation is decent, so you should be able to stay decently quite for most use anyways.  I know there's always an urge to crank the sound up, and with many earphones this works fine.  This is just one of those earphones that you really shouldn't.  It's something I always suggest for the C700 too simply because the bass gets really messy at higher output levels.  If you really want to go loud, there are other options out there.  The Nuforce NE-7M is one.  That's an earphone that uses a driver with a considerable amount of throw.  It rolls off bad on both ends though and has an annoying response peak at 5kHz though.  I couldn't stand listening to the NE-7M without EQing, but it's one that can offer an excellent amount of output cleanly for a pretty cheap earphone, and it doesn't need much wattage to do it either.

I've been using triple flanges on mine so isolation is fairly good. For some odd reason I can't get any of the tips to work for both of my ears comfortably. It's always one ear is good while the other has a horrible time. I had the same issue with the M6 when I had them and not with any other earphone...maybe I'm not meant to own a meelectronics earphone I get the best sound with those tips as well.
 

Well, you can always use some foam tips and make your life easy.