Same here. Nothing but trouble. Bought GPS Speedo, Tach, H2O PSI, head temp, volt, and trim guages. You do the arithmetic. Not just a buck or two, doncha know.
Volt gauge read 2 volts low from day one. Told them about it and they had me send it back for service. They tested it, said it was 'within tolerance', and sent it back. I have 3 other boat volt gauges and 4 DVMs that all show the right voltage. Go figure.
Tach was flakey at higher RPMs from the get-go too. Finally quit altogether. In their defense, they WERE able to see the problem with the tach and sent me a new one.
2 defects out of 6 sounds a bit high to me?