I know this has probably been beaten to death. But I hate re-reading old and possibly outdated threads.
I currently have a 2 battery system that is on a simple disconnect switch, both batteries on, or both batteries off. On my old boat, I successfully installed and utilized the perko "all, 1 or 2" battery switch without ever encountering a problem in regards to being stranded with my starting battery dead or worse, both batteries dead. I just switched to battery 2 (house/deep cycle that powered all the stereo stuff) when we were floating/listening to music.
SO... is a battery isolator really worth it? I like the idea that you can just forget about i, but is it really that easy? Is relying on something complex like a voltage sensing relay that reliable, certainly these have an increased likelihood to fail versus a simple switch. Is it work the extra $100 for something like the blue sea system. That extra $100 could go towards a really nice house battery ;-)