fcs keys, 2mm allen screws & the design of their fin attachment is not crap. The problem is the punters using it. They overtighten them. Or worse, don't put the 2mm allen key firmly in the hole when tightening or loosening it - therefore trashing the key and any screw it touches in the future.
Whenever you have a metal screw or whatever screwing into another softer base material be it plastic, fiberglass or whatever you have the very soft material getting a very tight grip on the hard material. Because it is flexable.
This (I think) with fcs sockets is compounded by U.V. over time hardening the plastic fitting over time and almost welding the little 2mm screws in tight.
The lession I've learned is....lubricate the screw with light oil, grease, crc, vaseline or something and then put it back in the thread. Use a quality high tenstile 2mm allen key...not the cheap fcs supplied key. And you'll never ever strip a thread.
If you already have done so. Bad luck. But it can be fixed. Go to an engineering shop & buy a 2mm drill bit. Buy also a small bag of 2.5mm grub screws with allen heads. Buy yourself a quality 2mm & 2.5mm allen key while you're there.
Use the 2mm drill bit to drill out the trashed screw, screw a 2.5mm grub screw in it's place (the extra .5mm will cut a new thread on its was in). Likewise put some oil or other lubricant on all your other fin screws...so it won't happen to them. And don't overtighten. Simple.