Do not buy used? Why not, where's your logic coming from here? Not trying to flame you I am just wondering why not used, its not exactly a high wear part, It's a carry handle sight.
Many people buy flat top rifles throw an optic and BUIS on it and then sell the carry handle which is essentially brand new on the EE but list it in the USED section. I bought one myself from there and it's served me damn well. Buy used, save you're money since you will most likely end up buying a BUIS at some point anyways. They tend to go for about 70 bucks but I have seen them as low as 50 and has as 110. Watch the EE and you'll have one in no time. Agreed about the name brand though, there are Tapco ones out there for like 40 bucks and they will not hold zero, Bushy, Colt, DPMS, RRA, STAG/CMT, they will all serve you well.
Stev