Back when I was driving OTR trucks, I had talked to several people/drivers that were using them, they said they loved them, worked great, but apparently some older design or something had issues when the mileage got high on them, where the beads or whatever they were using would clump up in the tubes or just not move around freely enough or somthing,, I dunno, it's been a bunch of years since I have been around it now though.
Supposed to work real well especially for dual rear tires.
Never heard anything about them being used on smaller tires like our trucks though.