All TPMS systems recommend changing out your OEM rubber valve stems to all steel stems. The transmitter weight causes a "whipping" effect on the stem and rubber cannot take it over time. You will probably have valve stem damage if you don't.
The sensor weight never effected the balance on my tires, and I used a system on a motorhome and a Honda CRV toad.
My MH was 38' long plus the length of the toad and I used 10 sensors with usually no problems on receiving all the signals. Every now and then one of the sensors would seem to act up and get a mind of its own. I had a few times when I considered the system to be a nuisance.
You should be able to cancel out the sensors that are not being used. I could on my system.
I used a very early Doran system and it was one of the first systems on the market. Now there are plenty more. If I ever bought another system I would try to do my homework and watch reviews. I see now some of the new systems allow you to change out your own batteries. With some you have to send in the sensor and have the company do it. Overall I liked the system and it was nice to know that my toad was monitored. There were also a few times when I wish I did not have to mess with the system when one of the sensors acted up. I havent convinced myself to get involved with another system (yet). Probably the biggest nuisance was in the wee early morning hours when the outside temperature would drop down and cause the tire pressure to decrease, activating the monitor alarm at 4AM in the morning.
