we have a few good Builders of 21's out..ask the guys who have them and shoot them to the tune of 3000rds a month. and ask them if the guns run with out a hick up.. as for Quirky...only if they are not done right.21's are quirky guns, not for the mass builder.
I have many Vector guns.
I would not trust them to turn out a 21 without many 'issues'.
If you're going to buy a 21, my advise is to blow the extra coin and get one built by a reputable builder (TSC, RDTS, etc). You'll be glad you did and you won't have to iron out the kinks. I have 1500 rds through my TSC 21k with ZERO malfs of any kind.