10mm may be great for a woods gun, but there is a pretty serious risk of over penetration. Imagine shooting that round inside a small store, that thing will zip straight through a person and anyone/anything behind them.
Try shooting that round at night as well, it's pretty blinding. I have a relative that used to carry a colt 10mm until I had him shoot it at night and demonstrated the penetration power of that round.
Don't get me wrong though, i love shooting 10mm and its my go to outdoors gun. I agree with the others that the longer slide is helpful.
1) Regardless of the round you should never rely on the threat to stop the projectile. You want penetration in order to cause the damage needed to stop a threat. Hoping that the threat you are shooting at is going to make a good backstop is poor judgment IMO. Quality SD ammo, ability to accurately place rounds on target, and proper situational awareness are required regardless of if you carry a 22 or a 44mag.
2) 10mm is powerful but it is not going to just zip through anyone or anything.
3) Quality self-defense ammo does not have a significant muzzle flash, even in the short G29.