We have the TST 507 with flow thru sensors, mounted on rubber stems. Metal stems will not fit on our wheels. We have 11,000 miles on these with no sign of weakening of the stems. Yes, there is slight movement as I've seen some small wear marks on the sensor cases where they touch the rims when the wheels hit bumps.
We find the pressure readings interesting. If you pump up the tires in the dark and then the sun rises, we see a 1-2 PSI difference between the light side and the dark side of the trailer. Then out on the road we see significant pressure rise as the tires warm up.
Our system also measures tire temps, but those measurements are meaningless. I measure the tire temps with a laser temp gun (bought from HF for about $25) whenever we stop somewhere. The temp readings from the sensors bears almost no relation to the reading from the gun.