Naim "based" preamps - yay or nay?

I'm a big fan of Naim products, have listened to them a lot as my parents have some of their integrated amps. But I don't have that kind of budget for them. I've noticed, however, on ebay there's a lot of preamps "based" Naim boards (E.g.  Hifi 152 base on NAIM NAC152XS;  C5 base on Naim 152; etc; etc). While I'm assuming the quality wouldn't be as good as an actual Naim preamp, can anyone speak to the quality of these kinds of Naim based preamps in general?