I've never used Erudite before, but from reading the description it has a different method of using powers. It has a column called Unique Powers Per Day, this is its big thing. What happens is an Erudite can manifest any Psion power, except the total number of different powers manifested in one day cannot exceed this number. For instance, at level 2 the number of unique powers possible is 2, this means that in one day you can manifest any 1st level power twice, but once you have manifested two different powers, you can only remanifest those two. You do not have to make the choice that locks you into something before you actually manifest.
I hope this helps.
Factotum can do a little of everything, but I don't know too much about it, so I'll leave this to someone else.