Hello,
I have always got mine from Andrew Page motor factors who generally supply the trade. You get a proper unit that would 9/10 times be supplied to the dealer. Expect £60 - £90 for the real thing, this would come in the body and on some models you get a refund when you return the old unit. Some ebay units only come as meter unit only, I have also heard mixed reports, I bought one for a VW van from Ebay that i was due to sell, it was replaced about 6 months later with a genuine Bosch from Andrew Page as it sometimes did not read with the ECU - its still going well - even after 20K of hard abuse. Check out the website for their local trade counters. Hope this helps