You can rely on them . It's what decisions do you make based on the data they give you.
Would you attempt a 100m entrance in zero visibility with gps? Gps plus radar? But what do you gain by doing so and what do you risk? Whats wrong with heaving to till dawn anyway?
These are human decisions that too many get wrong.
Just GPS that's one source, GPS and Radar, better, but that's 2 sources. It's night, so eyeball is no good in an unlit entry.
GPS and Radar agree, and fwd scanning sonar all agree with chart? I'd still be reluctant 1st time through there at night. Might try it in calm conditions, if any of those things disagreed at all, no way.