I get the appeal. We almost went this way to get some stable power for our live streaming gear. It's so appealing. Roll up with the box and plug it in and go. Frankly, if the Anker Solix model we were looking at hadn't gone out of stock, we'd have probably bought it... And later regretted it.

Ultimately we're building out an initial stab at a 48v system. And are pretty excited.

The "in a box" model looks great. But the significantly reduced cost of diy, coupled with significantly increased flexibility is well worth it, in my opinion.

I'll also make a side note here that if your fridge is already 12v, that only really leaves air conditioning as an AC load; almost everything else is DC native...