I have 7 myself don't tell anyone, 3 are GDroom only, two Net Dimm Firm Ver.4.02, two Ver.3.17 but I like to have two of each unit when possible. like you said if they fail they are my backup. I try not to throw stuff away I have a dead taito x2, blue cps2 A board, capcom I/O and cps3 motherboard. I would like to get them fix but I don't know-how and there seems to be no one nowadays that want's to take on that type of work