I've found that PlayerUnknown's Battlegrounds (opens in new tab) is a difficult game to get better at. Its firefights are sporadic, which means you don't actually get much practice shooting its guns. You can, of course, drop in a heavily populated area at the start of the game to get in on the action but that doesn't let you practice any end-game scenarios, such as firing a fully-tooled up sniper rifle.
I suppose it was only a matter of time until a game like Battle Royale Trainer came along. The idea is that you customise bots, choose your equipment, and drop into a small arena, ducking behind low walls or trees and spraying bullets until all the bots are dead. Developer Trickjump Games has avoided mentioning PUBG on the Steam store page (opens in new tab) but the resemblance is obvious, right down to the way the weapon scopes look, and all the guns are the same.
You can play in an urban or woodland arena or jump onto a firing range to get a feel for recoil and bullet drop. As you can see in the trailer above, the customisation of the bots is pretty extensive, and you can set their reaction time, accuracy, equipment and movement level. As you shoot them you'll see numbers spill out of their bodies, indicating how much damage you're doing, which is a useful thing to learn for PUBG matches.
The Steam reviews are mixed so far (opens in new tab), with some players saying it's simple but effective while others complain about bugs and misbehaving AI. Multiple players have said the recoil doesn't match PUBG's guns, which is a shame, because that's surely one of the main things you'd want to practice. It's something the developers might want to address in a patch.
Now, I can't help feel that there's something seedy about buying a game just so you can practice getting better at a different game. But perhaps that's PUBG's fault: if it included a mode that let you practice firefights, then Battle Royale Trainer wouldn't exist.