I don't know what JohnnyGrey's plans are with his device, he has only announced that it is not open source. But there are a number of people working on the open source mpguino . The goal of that project is to put fuel consumption feedback into as many hands as possible (read cheap and easy), so if you take a look and post over there about where we lost you then you would actually be helping too
http://www.ecomodder.com/forum/showthread.php?t=2115