What are the "small" flaws of the m10
Don't get me started on the stereo imaging from the closely spaced built-in omni mics (else forum members will yawn noticably).
I'm not especially a fan of the built-in mics, either, but then, I never use them for music. (For interviews etc., they're fine.)
After using an M10 heavily for a year and a half, I'd say the only things I'd characterize as flaws are: 1) the gain wheel can be turned when the device is on hold, though it's pretty hard to do so accidentally; 2) the auto/manual mic gain switch can be flipped accidentally, but it's immediately noticeable on the device's screen (big section of it suddenly is white-on-black text) and can be prevented through a small piece of tape, 3) transferring files via USB is moderately slow. None of these are dealbreakers for me, and none has ever even caused me the slightest problems, but I've noted that they could be improved.
In any event, the M10 could emit death rays that kill puppies and I'd still use it for its battery life alone.