Casey, I've got both Gen I and Gen II SmarTire systems.
Overall, they're great, and have saved me tires twice (caught repairable leaks, a puncture and a broken valve stem, on the flatbed), and prevented consequential damage by giving me instant notice of blowouts (twice) on the fifth-wheel, as well as warning me, through high temps, of progressing damage on the fifth-wheel (managed to stretch out an additional 400 miles by slowing down and doing frequent water quenching).
I do have trouble maintaining continuous signals from the trailers; the Gen II system is on full time on the truck, and almost never loses signal.
The Gen II system can monitor 20 tires, but the sensors only read up to 67(?) psi. They're still useful for monitoring temperatures, and at least the fact that you're over 67; however, the 'corrected' delta-pressure function doesn't work above 67 (it calculates what pressure you should be at, given the tire's temperature).
I have the Gen II system on the truck, and on the flatbed (which has P-series tires). The fifth-wheel has Gen I sensors (good to 110 psi) intalled, but they're not compatible with the Gen II receiver, so I have to use two displays when pulling it. The Gen I display is only good for six tires.
Doesn't quite make sense--the system that cam monitor 20 tires is only good for low pressures, and the one that's good for high pressures can only monitor six tires. Hopefully they will (or maybe have by now?) come out with high pressure transducers for the Gen II system.
It's not very clear, but the receiver is visible through the lower right quadrant of the steering wheel here...
#ad