Hello Dave,
I have wondered about the reliability of these devices, and on balance decided not get any.
For years we have managed quite well with out them, and in fact by having to check teh tyres by hand at the begging of a trip, you cna learn a lot more than just the pressure is ok.
A quick look tells you if you have any cracks or bulges, and if you have enough tread,
If all the tyres are up to pressure - then you know you dont have any significant leaks.
If all the tyres are a little soft especially after a long lay up, then that might be expected but if one or more is signifcantlt down you know theres more to the problem and it should be investigated further.
As far as I can think the only advantage a wireless pressure emonitoring system has is if a tyre starts to go soft whilst traveling. It won't stop a catestophic failure. which will be evident from other senses you get whilst driving.
I put them in the same class as tyre rim bands, No real harm in fitting them if you have the spare cash, but they dont replace doing the proper pre-jouney checks, and maintenance.