We used this service on our first full day in Bangkok.
Our guide Jean was informative and his English was very good.
We did the usual sights Grand Palace, Wat Arun, Reclining Buddah and Jim Thompson house. Guide Jean was at our hotel right on time (10am ) and we were back at our hotel at 6pm, we travelled by taxi, boat and sky train.
Lunch was at a local restaurant and throughout the day Jean never rushed us or pushed us to keep moving. This is a very good service and I would recommend Guide Jean to anyone who would like to use a private guide.