Is there a difference? From descriptions of how they work they seem similar.
Glucomannan forms a pretty thick gel when in contact to water, Psyllium husk just swells up a little.
The former is an insoluble fibre, and the latter (I have heard) is a combination.
As for effects, Psyllium has worked wonders on my pooping skills, and Glucomannan has worked wonders on appetite suppression.