Cleon
Legend
This ought to be a magic beast then. The text doesn't explicitly mention how the leech benefits from the drained power points, ie. converted to hit points, etc. Also I think a brain mole might be a better model since it doesn't need to touch its targets and it has the power leech PLA.
Firstly, they have a "Diet: Psionic energy", so presumably the power points act as nourishment.
Secondly, it says they use the power points to power a psychic blast:
Removing the creatures from their chosen hiding place is even more difficult than finding them. When touched, psionic leeches release their energy in the form of a psychic blast that causes 1 point of damage for every PSP stolen by the leech in the last 8 hours. Mental defenses such as tower of iron will or mindblank can reduce the draining effects of the leech or the damage caused by its psychic blast by half.
Thirdly, a leech satiated on power will reproduce:
Ecology: Psionic leeches bloat with stolen energy until they become too large and fall from their host. At this point they slowly crawl to the nearest wetland and give birth to 1-6 more leeches in 3d4 days.
Seems pretty clear.