I have a couple of Extreme metal mazes, a Green Obsession and the two V2 Obsessions with Extreme sleeves,
The all metal mazes are great, there's loads of feedback, but you start to ache very quickly while using it, though you do get used to it, I have the trainer from Revomaze and Alex's mapper, and they both provide bigger area to grab, which definitely helps with the aching/cramp prevention.
The all plastic obsessions I have found (bearing in mind I only have one)that they don't provide as much feedback as I would like when coming to ledges/traps, but they very light and don't take as much of a toll on your hands, though getting hold of these seems to be pot luck unless you know anyone who is selling.
The Extreme/Obsession Hybrids are a great middle ground, they're nice and weighty, but not so heavy that you can't play for extended periods of time, they also seem to provide a nice amount of feedback when falling into traps, with a definite audible click which I think is dulled down a bit in the plastic obsessions.
Also, they're a bit cheaper that the metal mazes and I think that they're a great introduction to the series
But I have to agree with Alex, nothing is the same as the Extremes
