We (family of 4) booked a trip through TripAdvisor to visit the recovery center. First of all: booking through TripAdvisor was very easy and we were well updated regularly. I also believe the price was competitive.
We did not know what to expect from this trip and worried about the distance from KL to the center. True, the trip is long (2x 3-4 hours), but it is well worth it. The local tour operator and driver were very professional, well informed and the car was specious for 4 tall adults).
Arriving at the ferry to the center, it looked a bit surreal: there is a large lakeside landing and infrastructure, but it was empty and there were almost no people. We took the ferry and once we arrived at the recovery center (group of around 10 persons), we got briefed by our tourguide. We walked in a cage tunnel complex (a reversed Zoo: the apes are free and we were in cages) to see the apes; we were allowed to help feeding them and got amazingly close by the orang utans. There are about 15 apes, including some cute young ones. Our tourguide explained what they do to return the apes back to the wild: most apes are abused animals, recovered from poachers or were used as pets. They all do this without any goverment funding and depend on private donations, struggling to get by.
So we really recommend to go on this tour through TripAdvisor, if you are not afraid of a 3-4 hour trip (both ways): go there and donate to the Urang Utan recovery center.
Also: on the way back to KL, you visit a nice Buddhist cave temple with huge Buddha's with a long climb to the top.