We booked in advance for four nights. Sarteneja is very quiet and there is not so much to do if you don't book a tour. But the tours were quiet expensive so we just did one. (Jungle Walk - was very intresting and Leo, the guide knows a lot). But the people in Sarteneja are very friendly. It is save and the food was cheap and good. There is NO ATM! So take enough cash with you.
To the cabana we had: it was very small but ok for a couple. The shower had just cold water so we used always the public shower. We had some strange stains on our blanket. Also there was a fire in the middle of the place all day (and night) long and we had all the smoke in our cabana.
The kitchen was small and not very clean and not well equiped. Can't understand why there is no hot water.
But the backpackers is well located in the jungle, very quiet and nice. You can take oranges from the tree or other organic foot for free. Also you can rent bikes.
Nathalie was a very friendly and helpful person. She makes everything that you feel comfortable.