I have an S shaped tank that is currently going through a fishless cycle, but it does have several plants in it. When I am more than 2 or 3 ft back I don't really notice any distortion at all. If I get up too close to look at something I sometimes have the feeling that I am wearing someone elses glasses, but that is only if I am trying to focus on something small like a new leaf or checking rocks for algae. Overall I really like the look of it and having varying widths allows for some more creative aquascaping.
Hopefully someone with fish in there fishtank can speak to how they look
EDIT: One other thing I forgot to mention. I have two heaters in the tank one at each end and the heater on the "fat" end does look bigger than the heater at the "skinny" end. So I guess there is some magnification. Still I think the unique design is a selling point for me. YMMV