Electric all the way. 3yrs on same gauge. I question the whole accuracy thing, you don't need to bleed an electronic gauge. If you leave any air in a mechanical gauge it's no longer accurate. Not that it even matters, does it really make a difference if it reads 10 instead of 11. 5? Especially on a gauge that reads 5-10-15-20 ect. Most use them to show they HAVE fuel pressure not the exact fuel pressure, it's not scientific.
Mechanical
Several fittings, lines, isolator or needle valve, gauge. Been there done that, never again.
Electronic.
Screw in the sending unit, run one wire in the cab, DONE!