I've been a member for about 3 years now. I've never been charged for anything I didn't want to be charged for. You just have to make sure you log onto the site once a month and tell them whether you want your "featured" movie. It's usually whatever big release Disney has going on at the time.
I have young nieces and nephew's so buying the five titles over the 24 months wasn't an issue for me at all. The "featured" movie is usually regularly priced so no real savings there, but they do run quite a few special offers. Like buy one movie at regular price and get all other movies purchase with it for 60% off.
At this point since I've fullfilled my membership obligation I can cancel at any time and I no longer have to get a movie if I don't want to. I get special "VIP" deals from time to time.
The shipping charges stink (they'll give you free shipping on featured titles sometimes) so I usually wait until a few movies the kids want have come out and then buy in bulk. For example when I switched to blu ray I picked up all the Pixar movies for myself at a fraction of the cost thanks to a 60% off deal. And they ship sloooooooooow. Really slow.
You can also get a free pin with every purchase as long as you remember to add it to your cart.
It's run by Disney (I had to call customer service once when someone stole half our blu rays at the post office, they mailed out a replacement of the missing movies without issues) so it's legit.
Honestly though if you already have a lot of Disney films it would be cheaper to just go to Target and get the new releases. If you're starting a new collection or buying a lot of movies for family then it can be worth it.