Just thought I'd update this old thread... I've had a Doran system for over 4 years now and am happy with it. Initially I mounted the front sensor inside the tire because there was no room for it outside on the FJR, and interfered with the brake calipers. Since then, I have the T-stem valve stems from tpms.ca, which allows me to mount the sensor externally and vertical so it runs between the brake calipers. The advantage is one can adjust air pressure via the T part, and not have to remove the sensor to do it.
Sensor life - I have had two sets of sensors, each lasting just over two years & about 3 months. Initially I had left them installed during winter storage in the cold, and was informed they are always transmitting as long as they see air pressure. This past year, I removed them for storage, but since that was for only one of the two winters they saw, I cannot say they really lasted any longer...... could be. Currently, my front one is OK, but the rear is almost dead as it rarely gets read by the display unit.
Today, Doran informs me they recently released improved life batteries after significant testing, however, the old price of $25 each has gone up to $35 for the new ones. I will install these when they arrive next week. Doran would like feedback on the new version......... I'm hoping that's 3+ years from now instead of my usual 2+ years.