Doc Football hit it on the head.
I was at the Great Eastern Outdoor Show last week and got to handle the r51 a couple of times. It felt good in the hand, until I squeezed the grip safety. With the safety depressed, the inside edge of the frame rubbed on my thumb knuckle at the web of my hand.
For me, I know it's gonna be a knuckle biter, so I took it off of my wish list, YMMV.
I recommend handling and shooting the r51 prior to laying down your hard earned dollars.