I'm looking at Carbines in 9mm and currently the MasterPiece and Cobray catch my eye. I'm looking at the 5" barreled pre-ban that will accept 30 round mags. I understand there's open and closed bolt guns. Not sure which is better. I notice that the MasterPiece carries a lifetime warrantee. Is there another contender? Are they easy to disassemble and work on? I can find many NIB pre-bans for $300 +/- $25. Thank you for your opinions.