I've gone through five tire changes... two front, three rear... and not a single problem. Two of them, the person used a hydraulic machine, twice another person used a manual changer like Harbor Freight, and once, I did it in the garage on the floor. The sender units are placed opposite the valve stem, and as long as the person knows where they're placed, then nothing more than a little caution and common sense needs to be used.
I do have a question as to the longevity of the units. I've used mine for over two years and ride almost every day. There is no hint that any signal is weakening. Within the first 100', there's the reading from the front, then the back... no problem. There doesn't appear to be any way to change a battery as the unit is one 3" grey slug. I've read that they last five years. Has anyone had a failure or a weak signal due to the battery going out?
John