The nice part about having an isolator is I can fully drain my deep cycle aux battery (like when I run a small cooler overnight when I go camping), then get up in the morning and still start the truck off the stock battery. Your setup will not allow that (although you don't want to drain those red tops down anyways, seeing as they're not rated for deep cycle applications and will quickly die if you drain them fully a couple of times).

Clean setup overall. I'm sure it will serve your purpose nicely, but for what I use my system for, an isolator and deep cycle battery are a must.