I would look for a system that allows you to change the batteries in the tire sending units. I had a TST system that worked very well, until the batteries started going. Replacing them required sending the senders back to the manufacturer. Instead I replaced the system with a Tire Traker system. I can change the batteries, but I have had a lot of problems with the senders cutting out, which makes the system less than worthless.
I may go back to TST, which now has a system with owner-changeable batteries. I am also considering a model that allows for adding air to the tires without removing the senders from the valve stems. Good luck with your search. As ryder said, now is a good time to change your valve stems to metal ones.