I’m also using CleanPage. Comparing the three, I like CleanPage best. It’s much more powerful, but it only has IE version.

http://www.ieaddons.com/en/search/?search=cleanpage

Good find. I agree with you about the ability to customize the size of the font and margins directly on each page. But what was interesting was the comparison of the visual presentation between the two programs. I compared Readability and Tidy Read using the federal government site that detailed how federal stimulus money can be used on “high-quality AT” and professional development and much preferred the way Readability presented the text.
It’s probably great to offer both options as different URLs will present differently.
(here’s the site if you are interesting, but being in Vancouver, this does not affect you – http://www.ed.gov/policy/gen/leg/recovery/factsheet/idea.html)