Mech will die on errors (read the docs on changing that, and under what conditions it doesn't do that), so in the default mode, you don't need to test for $mech->success(). But you do need to eval operations that you don't want to die.

Also, I have never used the back() method, so to avoid memory issues, I always set the stack_depth option to zero. It's a good idea to set it to something, as the default is infinity.