They are pretty much the same. "Performance" is not much of an issue with these calm water, high stability boats. They are heavy, predictable and slow but that is really all you are looking for.
My concern is that the prices you mention are way too high for used boats. I watch used kayak ads a lot and I would never pay that much for an older low-end plastic tandem such as those. I would say, keep looking for something more reasonable, offer them $400 or (if they won't come down) go to a dealer and see what sort of off season price you can get on a new kayak -- it will probably be at or even below what these CL ads are pushing. Cabela's (not know for the lowest prices) is advertising NEW Malibu 2 kayaks for $534. The Coleman is a discontinued model I have seen for sale for $350.
The only way that either of those boats would be worth even $500 would be if they are throwing in paddles and PFD's in the deal.
Full Size Sail Rig
PFD's (Life Jackets)
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