I haven't eaten at a FatBurger in a few years since I moved from Woodland Hills where I had one a mile away and not an In N Out in sight.
But back then I thought they were pretty good. Kingburger w/ cheese on the char-broiler. The char-broiled flavor alone gave them better flavor than In N Out. But yes, they were rather expensive. I can only remember paying full price once. After that, I didn't go unless I had a coupon.