I have a SIG Mosquito that has been pretty reliable with HV ammo with a bunch of different magazines, which was a departure from the original complaints of the guns being jam-o-matics no matter what was shot through them.
I love the feel of the gun in my hands, but the trigger and sights leave a lot to be desired. It’s not as accurate nor as easy to shoot as my Ruger Mark pistols, but it feels a bit more like a “combat” gun than the Rugers do...so for training it may be a bit more “realistic.”
A lot of fair to poor reviews on the GSG Firefly Model, just like when it was SIG branded as the Mosquito, so it may not be worth the hassles if you can find a more reliable and higher rated Taurus, Glock or Walther .22 to train with.
Stay safe.