I am putting in a 2nd battery on my boat and will need an A/B switch.

Is the field disconnect one (such as this one http://tinyurl.com/pa9hn )
always the way to go, or is the one that is $10 cheaper (but lacking field
disconnect) a better option? I do not switch to the other battery while
under power.....never have and do not plan to now. The switch will also not
be
out in the open for anyone to fool with.

So save the $10 bucks or get the higher priced one?