If you got them for as little as £120 it's maybe worth paying a bit extra to get them refurbished with new seals etc.
I got some PP calipers off ebay for a decent price (see main thread) but I've had problems for a while and I'm pretty sure one of the pistons is sticking. Point is, I've spent dead money on fitting the calipers, knackering discs, and now I'm replacing the lot with brand new calipers pads and discs. The calipers coming off will of course be getting a full rebuild before I move them on.
I just think for a little extra cash you can have the peace of mind that you're not going to end up with costly issues. I risked it, and lost out. Lesson learnt!