The 6300 was old tech which had "dirty DC" and needed the battery to filter it to be clean DC. The 7300 is a "switch mode" modern type like all of them now since about fifteen years ago or so, that makes clean DC and does not need any battery to filter it.
The 7300 is not worth the money because it only does 13.8v and you can get three-stage ones for less money.
The WFCO does 13.6 which is fine if you are only ever on shore power. Its problems are with going to its other two stages, so you can really only count on it for that 13.6, but that is all you need it seems. So it is all about money if you only want about 13.6v.
I am unclear what you have working now for DC to the fridge controls and lights , fans etc. You might not need new anything without knowing more. OTOH, you might have a problem that a new power centre won't fix. IMO more trouble shooting etc would be worth doing.
