What's the most accurate fuel usage gauge?

[fastegg]

Ive just bought a MPGuino.. 65 Euros (about $80AUS).. so when its up and running, i can start fiddling with things and it should tell me immediately whether its better or worse... woo-hoo...
The reason i'm happy is ive been waiting for years and years like 30 years!!! for an instrument that can give me immediate fuel useage info... woo-hoo...

[cbaber]

Where did you buy it from? All the sites I visited said they were out of stock or backlogged. Was it the kit or pre assembled?