Ok - so the item I went for in the end was the Michelin Digital Tire Gauge
A bit more costly than the competition but I already believe that it's the money's worth.
In the box was a note of instructions which are real easy to follow and a hard case which incidently is quite sturdy so I'm definately thinking it'll survive even the bumpiest roads in the panniers or wherever I decide to hide the little fellow.
Quite compact without being fragile
I went for a test at the local petrol station - set the pressure to 3 BAR (43.51 PSI) for the Continental 255/55 19" winter tires on the Pathfinder.
The digital tire pressure gauge from Michelin read 3.13 BAR (45.39 PSI) which equals a deviation of 0.31 BAR equalling that to PSI = 1.89.
Now....how reliable is this? How reliable is the digital gauge vs. the gauge on the petrol station?
I tend to find out!
Over the next couple of days I'll be driving out to several different petrol stations and garages to do some research and testing, jotting some notes down and doing some math.
Follow will come.
In general the gauge feels good in the hand. It's heavy and has a LED light at the nozzle if it's dark. It can be set to either BAR or PSI. It has an automatic turn-off function after 10 seconds and like stated above - comes in a tough hard case. You can "target" programme it e.g. for the rear and front tires of the car. The display is very easily read - bright and blue with the numbers being quite large.
The only down side I up till now can think of is that it's quite sensitive as to how tight and accurate you fit the nozzle. Thereby you have to hold it quite firmly and still against the valve. But maybe that's just untill it's been "broken in".
I'll present a follow up when I've used it some more!