I like it because it does my math for me, LOL! For my tip I used to just put in the amount of the discount, now even that is done for me - just sign the bill and leave. Very simple, and all-inclusive - but then, I always tip either the old 20% or the current 18%. OTOH, I don't do character buffets, so I wouldn't know about service there.
It definitely saves us money, FWIW. We are a family of 4 and make back our investment in a weekend worth of meals. YMMV, of course!