I was curious after reading your post so I checked out their web site and I am more than a bit skeptical.
The pricing on their web site for the going rate of fuel hasn't been updated since Aug.2007...
They are offering what I would classify as "diffently too good to be true" pricing. Gas (as of Fri. in S-SE Arlington was going for 3.82-3.84 per gallon....
They are offering units for 2.05 and saying they will reimburse you the difference...At todays prices that's 1.77 per gallon......
I don't see anyway they can do this and stay in business. Before I did anything I would check with the Dallas BBB. Where their P.O.Box is listed they give no physical address.
There is too much missing information here for me. I think it's a scam.
M.