All in all with delivery it was about 200 Euro, and it's a single gas tester (only CO). But it is said to be maintenance free. No cleaning, filter replacement, wearparts or anything.
It has a built in moisture separator.
Stated accuracy is about 0,5% but it reads in 0,1% increments.

So far only tested ONE engine, but it allowed me to "adjust the unadjustable" from the get-go, and I learned a bit about fuel linearity that I had no way of knowing otherwise (this engine has "accoustic" carburation (fully analog, no solenoid enhancements or anything), and with a bit of luck, I will be able to get an improved fuel linearity by tweaking the air restrictor that maintains fuel draw when the throttle opens.

Without that restrictor, the carb lost draw when the throttle opened, causing the mixture to lean out and in turn this required an overly rich mixture at zero load. Not good.
The restrictor cured that as far as I could tell, but apparently I overshot the linearity a bit. Gradually opening the restrictor while repeating measurements might result in an even better tunability.