It seems like anything with capacitors in it like this should be designed to limit the inrush when first powering up. Guess it costs too much and they feel it's better to just stick it on the end user to deal with.
As it is, my plan is to just hook the inverters up to a small power supply or battery charger of the correct voltage, with low amps and let it charge it's caps up from that. Presumably, this should work? The inverters capacitors won't draw more from the power supply than it's willing to supply.
I was thinking of having
something like this on a switch as my "precharge resistor". I just think the little screen would be neat, show you the amps the inverter is taking while it takes it and then show you the idle draw while the inverter is doing nothing before you switch to your batteries and then turn loads back on. It's so cheap it's almost worth trying it just to see what it does.