They all do the same thing, or there abouts. Just dont pay out for a Spoon or other branded one (unless you are a label whore!) as they are rediculously expensive for what they are. Some forum members make up kits for sale, around the £40 mark. TP and LeeH spring to mind.
got mine from funky power 25 quid delivered
LeeH does some good ones
got mine from funky power 25 quid delivered