well john,
dont fall into the trap of buying a cheap piece of crap from ebay. i did and basically i bought a yoke with a million and one features on it but yet the fm reception on the radio is brutal. i sent it back which cost 40quid and they returned it 2 months later with the exact same problem. ended up costing nearly 300quid with return postage etc. if i was to do it again i'd have a good look around at different branded units and i'd buy it from a shop.