Having had my 405s for 5 years on a 5.5m rib, ii cannot agree with most of your comments.
However, i did not have the space to fit a chatplotter and independant depth sounder display. I shirked away from a speed display as tge paddle wheel jams up very quickly with sea lice, and can be a pain to un-jam. The SOG from the plotter is much more useful.
My plotter could be configured in instrument mode which gave large readouts, at the expense of no chart.
At the end of the day i was more interested in what i might be running into, not what was directly below me. The 2m audible alarm gave me a good indication when i got there.
Fuses dont blow at random, unless the wiring is poorly installed, a common cause.
So if you have the space, fit a plotter and a depthsounder.