I've been using mine as my only battery for around three years now...never once had a problem with it. In fact, I'd recommend a large deep cycle as a primary to prevent the problem of draining a regular lead acid down to minimal voltage and not having it charge up again...
I use a yellow top for my daily primary. I have been for a little over a year, both in my Saab and my truck. Never failed to start, always has tons of power. Soon it will be my secondary with a red top for my primary.