I haven't tried the tv/movies yet....just being lazy.
I have not price compared, but even if not I love the convenience. When I think of something I need, I just go and add it to my cart. Then when I actually need it, or my cart has several items, I go ahead and submit the order for Friday delivery.
I also like that I can get free delivery (with minimum $35 order, I think) from Whole Foods and a few other grocers. I tip like 10%, but it saves me a trip to the store and the time picking.
Otherwise, yeah, you have to use it or you're wasting $100. I think they give you free 30-day trials, so you can go that route, too, and just stock up on a bunch of stuff and not renew/subscribe.