I have a pistol racket and I play with it sometimes.
I wouldn't use it seriously in a tournament or anything, but it's fun to play with. The backhand attack is a dream, in my opinion. I've never been able to attack so powerfully and accurately. If my opponent gives me a topspin or empty ball near the net, I'll hit it onto one of the corners at bullet speed.
I'm a backhand-dominant player (even with cpen grip) so maybe this is just me expressing my strengths.
I can serve pretty well on both forehand and backhand. Pendulum serve is quite good. There is decreased wrist mobility, but if you relax your grip you can deal with it. Usually I do not put my index finger through the pistol grip, and instead I use it to stabilize the back of the racket. If you do this, it increases both wrist mobility and control over the racket.
Honestly there is only one area of the pistol grip that I can complain about: the defense. It's very awkward to block with this grip, and that is the main reason that I would not play in a serious tournament with it. As soon as your opponent attacks, you MUST try to counterattack, because blocking is hopeless. It seems to me that from a physical point of view, the most stable blocking position is when you can put your wrist and forearm behind the racket, at a 90 degree angle to the racket. With TPB, this is very natural. With handshake grip, it is less natural, but still possible to get your wrist behind the racket. With the pistol grip, it is extremely awkward to put your wrist behind the racket.
