Please explain the features of Flexisheet that would put it in anyone shopping list. I could only find a domain for sale, a Sourceforge project with no released files and a CVS repository and also it seems only runs in Mac OSX.
About LyX, I guess most people wouldn't want it a little rough, wouldn't them? From the site:
It does look a bit rough, but don't worry, because the output will be fine
I think most people would want to edit text, not mathematical formulas for LaTeX and science papers which seems to be the main focus of this editor. It may be very good for that for all I know.