Some things to consider about many of the TPMS systems that mount outside the wheel on the valve stem:
- The caps are supposed to be lock nut secured, which means when you do ad air, you need to fuss with the wrench every time, twice for each cap, when you take it off and put it on.
- The pressure reading you get when you fire it up is the pressure from the last time you shut it down, not the current pressure. You have to roll ~100 feet or so before you get a current reading. So at the end of the driveway or block, you see you need air, and have to turn around to go take care of it in the garage, break out the tool, etc. (I'm not sure if the Garmin is this way. If not, that might account for it eating batteries.)
- Battery life/design. Some of the valve cap style allow easy replacement of the battery, others require you buy a new sensor as they have sealed batteries.
Only slightly related; Pet peeve about factory TPMS systems, they don't alarm until the tire(s) are already 8-10 psi lower than recommended pressure. The wife's '18 Equinox had the TPMS go off yesterday and was reading 27 psi. Normal pressure is 35 psi for that vehicle. So much for saving fuel! I have to wonder how long she's been driving around on the low pressure. She knows she is supposed to cycle thru the screens and check the tire pressure, but apparently hasn't been doing so. Nagged me about me checking the tires when she got her new car, "you don't have to, it has TPMS". We ended up stopping at a gas station and spending $3 in quarters to fill all four tires back up to 35 psi.