The Ospreys I have used, with standard .45 ammo, have been extremely quiet. You can hear the slide sliding and the bullet impact the target. If you're shooting steel plates, the impact on the steel is louder than the weapon being fired.
The Osprey can weighs next to nothing, and doesn't hinder accuracy and maneuverability, other than the fact that the pistol is now twice as long as it was before.
However, I would highly recommend raised iron sights, as the top of the can does interfere with the sights even though it's oblong shaped towards the bottom to help deal with this problem. It is designed to be used with raised sights or a red dot. However, with a little practice, I could hit just about whatever I needed to with standard sights.
Bottom line: Loads of fun.