I had one on my Saiga. It's just more ergonomic than standard AK grips, and they're cheap. Plenty of 'ergo' grips on the market but you have to be careful it's made in the US for 922 compliance.
they're cheap and some people think they look cool. I got one for my saiga because they're cheap and I don't mean inexpensive I mean CHEAP. if I could do it over again I would get something else. it's also a tad big for my taste.
One thing Ive found with trying the larger grips, and the main reason I use the stock grips on mine, is the larger grips can interfere with reaching the controls with your hand on the grip. They tend to shorten your reach.