I thought they were worth enough peace of mind to buy one recently... Went with the TireMinder system - but I'm sure others are good as well.
I monitor 6 tires on the RV and 4 on the toad.. (unit will monitor up to 22) While I certainly wanted to know if something was going wrong with the RV tires - not being in the toad I felt there was a good chance something bad could happen back there - and be made worse by continuing on... (didn't help that my last long trip was without my rear camera - thank you Jensen blank screen... even happier I had the TPMS.)
The simple 'disconnect' feature to temporarily disable the RV or toad monitoring (when leaving one behind) was nice... (of course the manual says if the toad tires alarm as missing - and you didn't knowingly leave it behind - you might want to stop and go find it...
Some options to consider:
Type of sensors - 'normal' or 'flow thru' sensors... I went with the normal - I have to remove them to add/remove air. The 'flow thru' allow you to add/remove air without removal.
Type of valves (applies to toad..) - cars with built in tire pressure monitors use a different metal in the valve stem that reacts with some sensors... TireMinder (and I assume others) make special sensors to use on these wheels.
Installation/setup was easy... A 12v powered booster to place (mine is in rearmost utility storage bin tapped off the light power - unswitched). Then setting your config (number of tires and positions) - and placing each sensor on so the unit knows what is where.