I had a six-month free trial of Marvel Unlimited, and I barely used it. I think I read about twelve comics in six months. When it came time to pay to extend the subscription, I cancelled.
I enjoyed the reading experience more than I thought I would – the interface was tolerable, and the art (particularly colouring) was beautiful on the tablet screen.
I didn’t use it simply because I forgot about it. Whenever I had time to read something, I reached for the physical stack of unread books and comics which is literally an arm’s reach from where I sit when I’m reading. The effort of finding a digital comic instead was (ironically) too great.
So I guess my answer is “nothing”.