I did it with my sister. And we both thought it was very funny. For every place, if you want it, there is also a story that you can read through. However, I have to say that if I hadn't already known a bit about Dresden, we wouldn't have made any progress at one point. But somehow it was also funny ;-) altogether we needed 1.5 std. But they also ran fast. I can recommend it and would do it again!
I thought it was great. We could start our tour through the old town of Dresden completely independent of any times. There was a lot described about every marvelous thing. If you take part in a "real" city tour, if you are lucky, you might have a few more interesting anecdotes, but it may just as well happen that you are unlucky and everything is much drier. The "puzzles" that gave the hint which is the next envelope were very easy, but everyone should be able to do the tour properly and see all the sights. All in all I can only recommend the scavenger hunt and would do a tour with it again.