I've had a Schwalbe presta-only digital gauge for a couple years and had no problems. Since it's presta only, there's no central post, just a rubber gasket that surrounds the knurled presta piston. It shuts off after about 10 seconds of non-use so it saves batteries. I've had the same batteries in it since I first bought it.
With all heads, whether they're analog, digital, stand alone, or on a pump, you have to insert it onto the valve as quickly as possible to minimize air loss. When checking pressure, I'll only unscrew the presta valve 1/2 or 3/4 of the way, minimizing the amount of shaft that exposed and unsupported.