Central air: Unico vs. Mr. Slim

I live in an older Victorian in the Boston area. Either a Unico-type system or a Mr. Slim-type system seem to be my best options. I'm thinking of having the system installed in the third floor (two bedrooms, playroom, and bathroom, in total approximately 1100 square feet) because it'd be far too expensive to do the entire house.
Any opinions on the relative merits or either system? Or approximate costs?
Many thanks.

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