We did the white water rafting but not with Mambo. We booked directly through the ship and they used Rio Tropicales....Class III rapids on the Reventazon River. This was my first time rafting and I had a blast!
You can check out their website:
The total tour was prob ~6-7hr long. Bus there and back ~1 1/2 hr each way...2 1/4 hr on the river....the rest was @ the center, first, for the briefing and then back for showers, changing (be sure and bring a change of clothes...you get soaked!) and lunch!
If you book a rafting tour be SURE to wear strapped
sandals, old sneakers (again.. you will get soaked!) or water shoes...do not wear flip flops. They will tell you to buy water shoes...their price is a little high @ $14.00 each. Also if you wear glasses be sure and have those straps to hold them on (hello!...they sell these too!)...or if you can do without, don't wear them...they get all wet and you can't see anyway! I wore mine and it was a pain! (it was also raining so that didn't help!) Half the time I was looking over the top of them! Oh...and don't forget the waterproof camera! If you don't want to bother with a camera, they have phototgraphers on the river and will sell you a CD of your adventure.
We bought the CD of our rafting adventure for $20.00! Good deal I thought!
Hope this helps!