vs. Meelectronics M6
Since getting HF5s the M6s have been my "gym" headphones. By "gym" I mean "sitting in the tray with the gym pass as I stare at both and think about going to the gym.. some day". Heh. I have the "Clear" version which satisfies my Secret Service fantasies, but really looks more like hearing aids.
Seriously though, the M6s are superb as sport headphones - great sound, no microphonics, and secure, comfortable fit. I find the MT-300s to be awkward to fit over-ear, and I'm not sure if that thin cable will stand up to getting wrapped around and snagged on things when (if) I'm active. The M6 also has a handy 90° plug which makes it easier on the wires when my phone is shoved into a pocket.
For sound quality though, the MT-300 is an overall better IEM. But it is close. I've always enjoyed the bass response of the M6 which extends well into the sub, yet has a bit of a mid-bass hump - a bit of a rarity. However I still think the MT300 has better control of its bass. Mids are also very clear and maybe even a bit forward. Going back to the MT300 after time with the M6 mids, vocals in particular, can feel recessed, but they're not. The biggest difference though comes in the treble where the M6 is easily metallic, maybe even harsh. The MT300 is comparatively smoother, and more natural.
However, for the gym I'd still be inclined to reach for the M6 over the MT300 just for its better fitment, zero microphonics, and suitable amount of bass to keep me entertained.
Here's a pic since we all love pics:
M6 has a JVC or Sony hybrid tip, MT300 has Monster Supertip foam