007Tacoma and maverick491 were recently loaned ECO-System VPE units to test on their own Tacomas. They concluded that the device does indeed improve fuel economy. They posted their results here.
Ben, from ECO-System, is offering Tacoma World members a group buy price on the device. The details are here. When ordering, mention you're from TW and you'll get the group buy price and free fedex shipping. Feel free to post your own results in the thread started by Mark (007Tacoma).