A little late in the game but I just purchased an M6 Pro. I am mainly a headphones guy and my daily driver is the Ibasso DX50 with Fiio E12A driving a DT1350. I wanted a cheapie in-ears that I don't have to baby too much, that I could use directly off the DX50 and I finally settled on a pair of these. This is just my humble impression of them and I hope I can bring something new to the table.
I bought them from Lend Me Ur Ears where I got to audition all the so called "giant killers" that people like to call these in-ears.
Here's a list of what I tried within the price range of the M6 Pro:
Vsonic VSD3
Havi B3 Pro 1
Vsonic GR07
Meelectronic A151
ATH-IM50 (from Jaben)
For fun I also tried their own brand IEM, the Alpha and Delta, AD01, with and without their "upgrade cables".
I tried their higher end offerings in their shop, although I am yet willing to spend that much on IEMs for now.
Kennerton Algiz (dark)
Dunu D2000J (wow)
FLC 8 (just as wow)
Getting back to the first 4 IEMs, I find the A151 nowhere near the other 4 made up of the GR07, VSD3, B3 and the M6 Pro.
The GR07 is out because it is more expensive the the other 3 by a fair bit.
I bought the M6 Pro mainly because it fits my ear better then the rest. They all have different sound signatures but frankly I think no one would go wrong with any of them. I would probably buy the Havi over the VSD3. The M6 Pro has a nice case that can fit both my DX50 and the M6 Pro which is great because it meets my needs of just pairing the M6 Pro with the DX50.
The M6 Pro can sound shrill out of the box but even though I kinda sit on the fence with burn in of every audio products, I would say there's some difference here, because the audition copy in the shop sounds nowhere like the one that I have. But after playing some music on the M6 Pro for about 2-3 albums, they sounded less shrill. But nevertheless the M6 Pro can be bright at times and if one is not averse to a little EQ then it an be easily solved by dipping the bars a bit from 3.3khz onwards by 1-3 dB at least on the DX50. So far it sounds pretty good with Daft Punk, Loreena McKennit and Hans Zimmer.
The M6 Pro runs well out of the DX50 directly and takes amping out of the Fiio E12A well, with or without the bass boost. For fun, I actually tried amping it with the Woo Audio WA6 but the bass just dropped out of it and sounded really shrilly. Weird, probably something to do with the damping factor but I have other 16 Ohm headphones that don't have an issue with the WA6.
By the way, I also accidentally bought a Zero Audio Carbo Basso from Amazon ( Damn you, One-click ordering!) and that should be a total opposite to the M6 Pro but that's a story for another day!
Disclaimer
: All in all for the price, it's really pretty good and the accessories make up for any other niggles. Bear in mind that these won't be my main phones, so I probably have a slightly more relaxed attitude towards their purchase. I am no audiophile and do not consider myself one and do take my impressions of them with much grains of salt. On the whole I am happy with it.