Firstly: they don't map over. Not even close.
Old forum thread:
https://groups.google.com/...QVh1HW8/n0GfOHRyoz0J Terrible machine, as far as I am concerned.
Dynamics: a bit more like 'real' rowing, but unlike real rowing, there is nothing happening in the first 12 inches of the drive. Again, I think they are a terrible machine, but they are an acquired taste. I had a bloke stay with me last year who has set several WRs on them and reckons they are fairly good.
Form factor is smaller than C2 C/D/E, but they can't be up-ended easily, so you lose a lot of space that way. I'll dip downstairs, where we store our C2s against a wall, and they occupy about 18 inches out from the wall by 20 wide or so. If you already have a C2, see if you can nose around for a set of C2 slides.
My subjective rating informed by years of erging and rowing and some coaching.
RowPerfect - far and away best, if you're prepared for: regular service, terrible form factor, and being pretty noisy.
C2 with slides - slightly painful to set up, and takes a bit of getting used to.
Regular C2 - standard, works, good storage
Dynamic C2 - hateful machine for the reasons I cited above.
Water Rower - nice piece of construction and sculpture, but not comparable.