I have a Sig Mosquito which is the same as the Firefly. GSG manufactured for Sig.
I've had no problems with mine. I love shooting it and use it as a carry gun at times.
I only use HV roundnose and have had no issues. I recommend using a quality ammo.
I like the fact that it has a hammer I can cock back if I so choose.
I put a grip sleeve on mine and it fits my hand nicely.
Has a nice weight to it. Accuracy is spot on.
Just remember to take the safety off before firing..it's a hammer block...
I once forgot the safety at the range and couldn't figure out why I was getting fail to fires.....3 times I dropped the mag and cleared it...DOH!
Once I realized what was going on I did a 2 mag dump out of anger at myself...