Ive got the TST system - never had a leak or problem
Have the sensors on the toad too...leave 'em on 24/7/365 - even when we're not towing the jeep I drive around w/ the sensors threaded on the valve stem....never had an issue.
I've got the TST 507 system with replaceable batteries...its a HUGE time saver....never have to drag out and compressor / air lines OR even a pressure gauge....just turn on the monitor to check my tire pressures.
i replace the batteries every 15 - 18 months (when i start to see one of the units stop reporting) -
10 batteries run me less than 4 bucks (38 cents per batteries, including shipping).
fwiw - TST does make an IN the tire sensor for those that think theres something wrong w/ threaded-on sensors.