OK. I took it out to the range today.
I have to say it equals the most mild recoiling 9mm I've ever shot. I compared it to both my Kel Tec PF9 and my Hi Point C9. The PF9 is my most "snappy" recoiling 9mm and my C9 is my most softly recoiling 9mm. The felt recoil on the R51 was similar to that of the C9. It's just a very mild recoiling gun, even with the comparatively narrow grip.
Even when I shot a few mags of Hornady Critical Duty 135gr. 9mm +P, I couldn't feel any real difference than when shooting standard Federal FMJ.
It points naturally and is more accurate than I am, though I tended to shoot just a little low with it. The sights are nice. The front sight seems huge in comparison with the others.
However, after about 8 or 10 mags through it, it started dropping the mag during recoil. It wouldn't drop free but would slip out about 1/16" of an inch. It did this reliably through about three mags before I got tired of thinking, "I'm just getting to practice my tap-rack-bang drills" and gave up on it.
There's something wrong. Something might have come loose but I won't know until I get it torn open to see if anything jumps out at me (literally or figuratively).
I'm really disappointed. If not for the mag drop, this thing would definitely be in my immediate carry rotation.

No, I didn't save any targets.
Peace favor your sword,
Kirk