I would recommend doing this tour first day on arrival in Zagreb because you will get to cover all the key sites in around two hours and those Segways are a lot of fun once you quickly get the hang of them. Then you can actually go on foot and explore in detail sites that interest you afterwards.
If you’ve never been on a Segway before don’t worry training is very good and quick should take you about 15 minutes to be competent.
The tour guide’s knowledge was excellent. We had Dora and she was extremely knowledgeable.
All in all really cannot fault this.