The same company has AFC, for $10, and it looks pretty good.
It has syntax highlighting
it shows the directory and file comparison windows at the same time
has in place editing.
I have not tested it, because vim does all that and more for free (vimdiff!), but of course I'd not recommend people to start messing with vim (although this one thing is ultra easy) if they need file comparison. Plus vim it doesn't do directory comparison (that I can think of!).