The Mt Vision wasn’t a TARA. The longer travel stuff, Attack Trail, Wolf Ridge, Rock Springs, were the TARA ones, adjustable 4/5/6in travel. The Mt Vision/East Peak were 4in XC bikes.
2004 were the first of the quad-link folded and welded ones I think. I really liked mine at the time, raced it until I bought the Yeti in 2009.
No idea which would be best for you, but a Mt Vision definitely fits very differently to a Genius, whichever you like you will probably hate the other. My mate who had a Genius never got on with the high BB of my Marin, I liked the ground clearance, he reckoned it cornered badly.
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To come back to your original question though, loads more Marins about and shocks are easy to change, no weird proprietary stuff on it