I was on SDD on Saturday. First, it's awesome!! So much fun...as I mentioned in the other thread it's fast enough to be entertaining, but not too fast to scare you (at least not people who can do moderate coasters).
Yes, it backs up. However, it's a very slow and gentle backing up. Imagine backing out of a parking space at a store and that's about the same sensation. It's gentle, slow and not far at all...maybe 5 or 6 feet. I can't see it bothering anyone. Then it launches again, but even that isn't hard.
It's faster, in my subjective seat-of-the-pants feeling, than 7DMT, but not much. It has a moderate size hill, but you don't go over it all that fast. In the second section, after the back up and launch, you go over a series of small hills, and they are small. It's fun. No, it never comes close to going upside down. Again, just going from memory (and trying to take it all in), but I think the turns on 7DMT are more steeply banked than what SDD is. You lean sideways some, but nothing drastic.
It's nothing at all like EE or RnR, not even close. Even BTMRR isn't quite the same, as SDD is far smoother. Maybe the best way I can describe the "intensity" is imagine 7DMT going 10-20% faster and you'll get the idea. Even that may be debatable...the more I think about it, I think it may be about the same speed as when 7DMT is at its' fastest point. Either way, they're comparable.