I moved to the M10 (because my R-09HR was destroyed) and prefer it, but only because of the better battery life, slightly better preamp, and the onboard storage capacity. I also don't stealth much.
If I did, I still think the R-09HR is better precisely because of the "HOLD" function that allows you to lock the gain. I also found the giant "RECORD" button in the middle much easier to find in the dark, without looking at the deck. And the M10s brighter lights (including the nice-looking flashing peak lights on either of the top corners), while desirable if you're not worried about being detected, are also a negative for stealth reasons.
I also bought into the whole "the level knob won't move" thing after many on here said that was the case... and then found out the hard way when it did move one time when I was pulling the deck out of my pocket to check levels. Yes, I know how to use gaff tape - but that seems like a less desirable solution than a "hold" button that actually puts ALL functions on hold.
If I still had the R-09HR, and if mine had not been damaged, I would not have moved to the M10. If anything, if it's sound that you're concerned with, and you record quieter stuff, you'd be better served by adding a Church pre.
All that said, the M10 seems better built and the battery life is amazing. So it's really just a matter of dealing with the REC knob and changing the setting for the peak lights.