Had a question at 11pm on a Saturday. The owner answered it immediately via email.
I also wanted to do a barrel swap from tri-lug to threaded but whatever loctite they use is a beast (heat wouldn't budge it). Owner had me send him all parts, they did the barrel swap, gave me a new extended handguard, sent original parts back. Only cost me shipping to Foxtrot Mike. They even covered shipping back.
I am in no way affiliated with Foxtrot Mike. These have been my only interactions with them. Their stuff works, they stand behind it, and they go way above a beyond for their customers.