I have mixed feelings regarding the TST 507. On the one hand it has succeeded in warning me about tires losing air. On the other hand it has caused the tires to lose air. Confused? Here's my story. I put the sensors on my Chinese made tires 2 years ago. Then I switched to a better grade of tires (Maxxis) and Discount tire put in the rubber valve stems and put the sensors back on. Last year we were coming home when the TPMS alarm sounded. Changed the tire and took it to a tire shop where they discovered a leaky valve stem. This year it happened again not once but twice. Same problem - leaky valve stem.
I discovered that the weight of the sensor and the spin of the tires was causing the rubber valve stems to fail. Their website says to use metal stems because rubber stems cause problems. I had a Dickens of a time finding a tire store that carried the kind of metal valve stems I needed.
The moral of the story is that while the TPMS protected my tires from further damage they were indirectly the cause of the problem.
The other problem is the short range of the system. I often experience a loss of signal from one of the sensors due to a weak signal or some kind of interference. They do make a repeater for this problem but I elected to pass on it since the signals eventually returns.
Overall I'd say go for it but make sure you have metal valve stems and be prepared to pay extra for the repeater.