I have owned one and own one now. All the target model is is a P22 with the 5" barrel, sleeve and stabilizer installed onto the frame. It cycles weaker ammo a bit better due to more blowback energy. The front sight blade is moved from the slide to the stabilizer giving a longer sight radius. The pistol becomes a bit muzzle heavy which helps with fast follow up shots. You can shoot it more accurately off hand.
The stabilizer has been problematic to me in that it walks, the old style and the new when firing 500+ rounds. You have to remove the stabilizer to field strip the pistol. It clamps onto the muzzle end of the barrel sleeve and barrel nut.
From a mechanical rest the target version is capable of sub 1" groups while the 3.4" barrel is in the 2" to 3" group range. 25 meters or 82'. I think a full 5" zinc slide might be a bit too heavy for reliable cycling but an aluminum one wouldn't be.
Something like this with 5" PPQ design cues. One piece. Aluminum. $300 out the door.....they can do it. 1917
My 2005 effort to show em the way. Umarex didn't bite then, probably won't bite now. They did adopt the three slots. But, Cabella did, they lifted the non-existent pistol photo from a thread and put it in their Christmas catalog. I hear it sold out immediately, so fast...no one got one.
I added the target kit to my 3.5" P22 but haven't shot it enough to notice a difference in accuracy but it has been completely reliable. What I have noticed is how front heavy it has become. I've found that I prefer using the 3.5" barrel and I'll probaby swap back to it the next time it goes shooting.