I was on the verge of buying a .25 R5M long.... after doing some research and talking to people, I ended up with a .25 Vulcan 2. The reviews on the R5M were very polarizing, i.e. people were either die hard fans or absolutely not. What I found is many, many people complained about the cocking mechanism. It doesn’t employ a true biathalon style lever utilizing mechanical advantage and the cocking effort is significantly more than that of the Vulcan or Wildcat.
I talked to a couple people who had magazine feeding issues with the R5M, but nothing major. Everyone seemed to praise the simplicity and ease of working on the rifle. The accuracy that I have seen both personally and on the internet was good, but nothing earth shattering. Along with the simplicity, the rifle is very very quiet in its stock form which is awesome. Adding an aftermarket mod isn’t really necessary for most applications.