Paul,
I do not know what the differences are between Mutiplus and Multigrid but they look to be almost identical so I'm surprised that Multigrid costs less especially by that significant amount.
It seems both have the Aux 1 and 2 and likely both have the assistant so it should work the same. So yes the Multigrid will work I'm 99% sure but you can ask victron if you want to be sure.
Strange that is that much less expensive for what basically seems the same inverter.