After just over 30 days of using this i can say that it may not be 100% accurate but it’s better than nothing.

 

All your tires are low according to your readings @2.3 should be 2.6(37psi). I check my tire pressures, by looking at the tires. I can also use a tire gauge, to check my eyes.

 

So, I have 3 of these (similar ones) in my vehicles and have to say the pressure readings are very consistent. All increase in PSI as the tires warm-up (as expected)

On accuracy, I have 4 hand digital gauges and 2 mechanical ones, none of them agree 100% with each other, although they're "similar" They may be crap, but absolute accuracy depends on so many factors, outside ambient air pressure, outside temperature, the accuracy of the gauge itself, plus each time you take a reading the pressure drops a little (not an issue with big Hummer sized tires)

Tire pressures should be set when cold, but what temperature "Cold" is is hard to say, I've read pressure rises 1psi per 10F, also sunlight on the tire wall has an effect.

I use the Hummer with a digital tire inflator, which clips-on rather than screw-on which save's time. I use the TPMS as the "standard" then calibrate the digital-inflator against that, in my case I know the inflator under-reads by about 1.5psi for the nominal pressure of 37psi (38.5)

PSI is preferable to Bar as 0.1bar is 1.5 psi thus the resolution is better.

Although the TPMS pressure readings are very consistent, the temperature readings are way-off, sadly I've not found away to calibrate these, so I keep a mental note of the values when setting off on a trip.

The most important things are repeatability and detection of abnormal changes, the point about TPMS is the "live feed" which is why (at least in the UK) this feature is now mandatory on all new cars.