We've been using the TST system (old version) on our tri-axle trailer for about 2 years now. I've got the opposite theory you do, I have them on the trailer and have been holding out on buying them for the truck. Theory being (from past experience) that I can blow a tire on the trailer and never feel a thing and don't know it unless I happen to be looking in the mirror when the belts are flapping, or somebody flags you down. The truck I can feel.
Anyway, the system works great, after an initial bout of sensor failures which they replaced under warranty with an updated version. The readout really does a good job of educating me on pressures and temperatures. I am usually on the edge of the tire weight rating, and it is amazing to see what a few miles an hour make in pressure and temperature. If I see things creeping up, I can back off a few miles per hour and everything goes right back down.
I figure the $300 investment easily pays for itself on a single saved tire. I have already had several occasions where the alarm went off for a slow leak (nails and such) where I was able to continue to a SAFE place to change the tire, and save the tire before it was ruined. Not to mention saving damage to the trailer from the tire. And peace of mind. I don't have to strain to keep an eye on the trailer tires in the mirror all the time any more.
Get those things on the toad, new tires or not you can pick up a nail at any time, and the investment is well worth the peace of mind, and a drop in the bucket compared to the investment in the unit. Keep in mind you need rigid bolt in valve stems to mount the sensors, the extra weight can damage the stems. I think the oem tpms sensors on the Jeep are bolt in deals, and you should be ok on that front.
Thinking of the inners, I have not mounted them there yet, but I am leaning towards the RV style stainless hose style extensions. My thinking is I am not sure if I trust the sensor screwed on the end of a really long rigid extension. I'm thinking that long assembly, while light, could put a lot of strain on the valve stem or loosen up. I'm interested in any input on that issue myself as I am looking to add them to the truck.