never known a pistol grip to fail on a cav-arms polymer. they molded theirs in though, just like the stock.
glad you beefed up the front pin and the buffer tube area.
to me it looks like it should be a little thicker around the rear pin hole , i have seen a "number" of super-polymers fail right there. i would have went much thicker and used a longer non-standard sized rear pin in that location. --but then i would have made the stock into it as well and it would be seamless on the stock to lower joint. but i like a 500% safety factor when i can get it.
what kind of plastic--er polymer are you using? can it be repaired if it cracks or splits?