[Greymagius]

I've a pretty good idea on 'Magic' and Sorcery for the BRP, but am curious if anyone can shed some light on the psionics system? I recall a psionics system from an issue of 'Different Worlds' for CoC. The powers were very low key, but well suited to a subtle game such as CoC. There was also a system in CoC D20, that was rather low key.
A few specific questions I have are:

Does BRP psi require skill or a stat based roll to use?
Do they require 'magic/psi' points based off power?
How do they compare to 'Magic' or Sorcery in usefulness?
Can they be improved and added to in play?
Is there an advantage in choosing 'Psi' over other meta-physical arts?

Any information wold be appreciated,

Thanks,
Grey