HaHa, I tried a plug-in tuning box for my Diesel VRs from a company that looked reputable and sounded knowledgeable at a car fair, I even went to their company premises and they seemed ok, did some before and after runs and made no difference, didn't even feel any different. Told them as much and they refunded my money.
Did
help me out though as needed a remap on my car to meet the carryover modified insurance I had a month left to run, when I replaced my tuned Audi A4 TDi for it.
On topic note, did the 'Track Obsession' Power 2 Weight shootout today and came away V.happy although was nether gonna win any prizes as some serious money turned up.
As it stands my Leon has a 49.5%/50.5% cross weight distribution and is approximately at 230bhp/ton. Was hoping for over 200 bhp/ton, so very happy. Next goal 250bhp /ton