Just wanted to throw in some caution, but I heard from someone at a previous San Francisco Bayleafs meeting that the system is NOT officially approved by Nissan. He had purchased the upgrade because the Enginer advertisement in an EV magazine had mentioned that was approved. Unfortunately, this is untrue. If I recall correctly, he later had problems with his car's charging system and Nissan would not perform any repairs as the car was modified without their approval.
I haven't verified any of this further as I wasn't interested in purchasing the unit, but a strong buyer beware should be heeded IMO.
edit:
Here's a post discussing that Enginer argues it does not void warranty because the "Kit installation does not cut any wires, and the car can be returned to stock state at any time. The company claims it does not void the Leaf's warranty."
http://www.evdl.org/archive/index.html#nabble-td4657414" onclick="window.open(this.href);return false;
I'm guessing that the whole thing would need to be uninstalled and the car returned to stock if warranty service is required, but who knows...