Just received mine today and installed it in my R700 SA stock. I had to remove the top plastic fitting and hex socket nut to get it to fit inside the grip. It is possible that with some grinding down of the black plasting end fitting you could keep those items on. I have an early version of the stock, so it's possible that newer variants will not have the interference I had.
Once the cap is screwed on, it seems solid enough. Not as fine as an Accu-Shot monopod, but a good deal for the price. The plastic bottom cap might slide around a bit. That could be good or bad. When you tighten the lock nut, it takes out the play and is decently solid. You will have to screw it in all the way to retract (no "quick knob" option, but again, for the price....
I have not taken this out to the range yet, so I will check to see if there is movement under recoil or not.