While I like the ERGO, vertical grip, I like this better -
The "Emperor Grip", which is modified with some epoxy to "fit" my hand.
https://www.anarchyoutdoors.com/emperor-grip-precision-rifle-grip/ It's also a vertical grip. I used some tape to seal off the big hole in its side, then put a big blob...of epoxy on the right side, then grabbed it as if I were shooting. This left an imprint of the palm of my hand in the epoxy. This way, my hand sets in the same position...every...time I hold the grip. The good thing is, if you don't like what you have done...grind a little epoxy off, and redo the procedure, until you are happy with your hand positioning.
Note that the Emperor grip by itself isn't bad either. Two (maybe three) sizes are meds for different hands sizes.
Then paint to fit.
And yes, this is...the same grip as the AR15 rifle, that fits MANY air rifles.
Mike
P.S. - ERGO makes two or three different angles of their grips if you don't like the vertical (90 degree). Just read each grips detailed info to find the grip angle.