I have used this taxi service; I called the day before and then called (unnecessarily) the night before to confirm; I was told very politely no need to reconfirm.
The taxi was waiting downstairs exactly at the right time.
The meter was running and was at 5-6 euros.
It was a Sunday morning from the 6th arr to CDG - nice Mercedes with a friendly driver and the cost was probably around 55-60 euros or so. I added a nice tip for driving slowly.
Highly recommend it. Try this link; they have service in English over the phone and an english version of their website.

http://www.taxisg7.com/taxis/commande-taxis