I'll keep my thoughts about the need for these things to myself, and just confine my comment to a little editorializing about their use. I strongly recommend that people do NOT substitute one of these devices for proper tire inspection on a regular basis. The good old fashioned manual inflation check provides an excellent opportunity for people to actually inspect the tires for damage, irregular wear like cupping, the beginnings of cracking or tread separation, or something like a screw in the tread that may not be leaking enough to notice now, but could be thrown out at high speeds and lead to a rapid loss of pressure and a crash.
I've heard or read comments from way too many people over recent years that they don't need to check air pressure in their cars or trucks because the manufacturer's have to install tire pressure monitoring systems in late model passenger vehicles. It's comments like those that convince me that way too many people these days are clueless and have no business on the highways with the rest of us. By the time those systems send an alert, the tires are usually 25% underinflated, which is borderline dangerous at best.
Jerry