That was us. We LOVED it. We did it our first night there (the night version - seemed right for the City of Lights). Lots of fun, and a really great way to introduce yourself to the city.
http://citysegwaytours.com/paris
Definitely recommend it as one of the FIRST things they do as it gives a brief look at lots of different parts of the city. It would give them a nice way to get oriented, and pick a few things they'd like to go back and see in detail. It would definitely not be as interesting if they'd already spent a few days seeing sites.