I would like to know the pros and cons of both, from the folks that actually have , or do own them. I read that the Smarty doesn't leave a footprint, and I emailed the folks at Poweredge, and they told me that the Mileage Max doesn't leave a footprint as well. Whether this is true, I don't know, but that aspect is very important, because I don't want my warrany voided by the dealer!! Thanks!!