Generally thought of as the definitive row bike seems to be the Thys, which looks a whole lot better designed and engineered than the one at the top of the thread to me.
By all accounts I've heard it's a very capable machine and riders have put in very good times on long distance sportive rides using them.
The main point is, I guess, for rowers to practise their craft without needing a body of flat water and without the incredible boredom of a static exercise machine.
I've ridden a conference bike around Dundee. It'd be nice if someone could do a lighter one. Rather than a conference we have a small hierarchical committee bike in the form of a Thorn Me'n'U2to get the kids about town and to school and back if they're not on their own bikes. It gets quite a bit of comment (almost all positive).
