We took the Paris Bike About tour last week. We joined a group of about 10 people and the tour lasted 4 hours, including a short break in the Latin Quarter.
The bikes were Dahon Vitesse (the derailleur version, not IGH). We went though bike trails as well as roads. Traffic was busy and the Paris drivers are very aggressive with very little patient for bikes (at least compares to the norms around here) but felt safe overall. Bikes where relatively new and reasonably functional though were far from tip top shape.
Our guide, which is also the proprietor was knowledgeable, friendly and spoke good English (a New Zealander). He came with his own bike, a Mu Su, and at one point offered me to swap bikes so I did the rest of the tour on his bike. The Mu Su we stiffer and lighter and I liked the single lever trigger snifter.
When we stopped at the Latin Quarter we had a chat about folding bikes and he said that he has difficulties with bike availability and prices (all his bikes are Dahon Vittese) and that he considered Bromptons but they are too expensive. He prefers small wheel bikes because of the wide range of seat height though they never fold the bikes.
Overall it was a lot of fun. In case you visit Paris and want to tour it with small wheel folders their web site is http://www.bikeabouttours.com