The fuel isolators might not show a 1 or 2 psi fluctuation quickly enough for low pressure use, but for EFI stuff it is worth it's weight in gold. I regularly put 150 psi of pressure thru my fuel system. The electric sending units cannot handle that kind of pressure, and are VERY scary when they fail.

Ever seen fuel boil while being sprayed directly onto the headers and not catch fire? No sparks allowed.