I can't quite believe this, but I bought this for £10 including postage:
Now I have real time display/graphs of all sorts of zappy engine parameters, instant or average mpg calculations, a trip computer and a ton of other stuff I'll probably never use.
I can read and reset fault codes, if I had any, but none have occurred in the 3.5 years and nearly 50,000 miles since I've had the car. (The ECU also has no historic fault codes stored - not sure this means it has never had any, or there just aren't any stored, and whether its possible to erase such historical data)
If I had a hat I would eat it, but I've a Pousin in the oven so I shall eat that instead.
Gareth.