My Multiplus-II 3000, when in inverter mode with inline GFCI and Ground Relay enabled, instantly trips the GFCI's on certain equipment (modern "inverter" heat-pump A/C's - a Midea-U and a Danby-U - I've seen on the web that the high-frequency multiphase motors give trouble with standard GFCI's, so the heat pumps have their *own* GFCI cords and claim you have to plug them into a non-GFCI outlet). My Samsung front load washer, an "inverter" microwave, some refrigerators, and an inductive hot plate all work fine with the MultiPlus-II.
I don't think it's safe to operate without GFCI's - is there any knowledge of these problems?