The DC-DC converter is adjustable, the same one could be used in a Prius or Escape Hybrid and the Escape is higher voltage. So it might work.
From what I've read, everyone seems to have issues with Enginer kits. It seems like they aren't very good at keeping the cells balanced. You better like the tinkering aspect a lot.
As far as return on investment (I understand hypermiling is partially a labor of love), the number crunching I've done shows that its likely not financially a good idea. Even if you doubled your mileage from 60 to 120MPG with gas at $4 a gallon and $6k for the kit (they don't have prices on their site anymore but I think that was it), it would take 180k miles to break even, without including the cost of electricity. Add in the issues people are having after just months after installing their systems, and it makes for a grim picture. I would try to trade in on an Energi, if anything.