We use Booking Manager every day. I like the possibility of having the access to the system from my mobile phone, so even in the evening when I am with my friends I can check the best offers and create direct options or bookings.
We always dreamed that the client could be able to get all optional extras in a few clicks. That was not possible until MMK introduced the XML service, which enabled us to get all info about current discounts and availability.
Booking Manager is one of our favorite partners, as the API data structure and performance is very good. We especially value the personal contact to the developers and their open-mindedness for constant improvement.