I own multiple of each of the older systems (I owned them, then my GF moved in and brought another) so I haven't played around with these OAC types. I've heard good and bad things. When they work correctly its great but as was said above, not 100% accurate. The last option (the 3 in 1) is appealing simply because if it works its covering 3 systems. As for the others, I'd rather just buy an original that I know will work 100% of the time.