I bought the TST 507 sensors ($350 for the monitor with 6 sensors). I used 4 sensors on my 38 foot fifth wheel and put the remaining 2 on the inside wheels on the truck rear axle (I have a dually). I have been VERY happy with them. I did not need a repeater to get the signal from the trailer to the truck cab.
As far as customer service, anyone who answered the phone at TST could help me with any questions I had, I didn't have to be transferred. When I was decided which model to buy, I sent an email with a question using TST's website and I received a return phone call from one of the owners!
On the subject of steel valve stems; if you are going to spend $350 for a TPMS, why not spend $5 each for steel valve stems?
