Explain Battery Combiners and GFCI vs. Galvanic Isolators?

Question:

I enjoy your articles in Pacific Yachting each month and also the information on your website. I own a 33’ sailboat and am looking at updating the AC and DC systems as they have evolved. The DC in particular has outgrown the original architecture. 1. Should I replace the 1, 2, ALL, OFF battery switch to incorporate an automatic charging relay (ACR)? I am starting with a plan to test the current switch to see if there is any reason to replace it. E.g. the contacts still as good as new! I have a suspicion that there is a downside to an ACR, perhaps if one battery bank gets drained, but I am finding it difficult to find a clear explanation of the pros and cons. To me I seldom run in ALL mode and switching batteries is second nature. However, I am hoping my daughter and family will start to use the boat and they don’t have that background. 2. Should I install a galvanic isolator and/or an ELCI AC breaker? My sense from Blue Seas who do not market the former, is that the ELCI provides similar protection and new protection. I have been unable to verify how true this is. I am assuming that the permanent battery charger (Xantrex) may well provide a hidden interconnection between the AC and DC systems.