No, but the springs and trigger from HBI work great. Not sure I'd want to get into another whole mechanism - the Evo is a proven system designed for the military.
I’m thinking in terms of the disposition of the “final” pistol brace rule. Though, I’m confident that the rule will be thrown out on Constitutional grounds (eventually), it may take some time, as we’ve seen with bumpstocks.
Though the 3+ Pistol is US-made and compliant, the S1s etc. are Czech-made, so you’d have to deal with 922(r) compliance if you lengthened the barrel to 16” and added a butt stock. $$$ PITA, I know, but 922(r) is still on the books and carries some substantial criminal penalties.
I assume this company is GTG, as they seem to make a lot of precision parts for high-end firearms, but have never dealt with them before.