Just to add my limited experience here:
My Rotax 912 powered aircraft was equipped with a fuel pressure gauge and I noted that the Facet pump only raised the fuel delivery pressure by one psi. The pressure remained well below the Rotax recommended Max pressure.
So far, so good.
However my fuel flow gauge showed a significant increase in fuel flow when the Facet pump was on. This remained unchanged after replacement of the float valves.
I mention this for the benefit of pilots who may desire to run the Facet boost pump continuously, without pressure and flow monitoring. The increased fuel consumption could cause flight planning problems when the tanks go dry a bit early.
Sounds like your pressure gauge is consistently reading low - non certified/calibrated gauges should only be interpreted as indicators and if readings are consistent (all other parameters OK) is probably fine.
I periodically record all my gauge readings (along with OAT & Alt - this gives a record that enables the pilot to make an informed decision's based on passed performance/indication.