Caecilia is the darkest serif font. The other serifs are terribly thin. Helvetica is the darkest font overall, but I really prefer reading using serif.

I installed Screen Dim but it takes a long time to initially get it set correctly too. The sample text shown in Screen Dim does not accurately reflect true screen brightness. So you have to keep adjusting it little by little. Once set then you can save the setting and not have to mess with it again.

Since I rarely use my Android phone for anything other than voice calls, text messaging, and groceries lists, I guess I forgot how much Android is a PITA, especially Amazon's version. But since I'll only be using the Fire HD for reading, once I have it set up it should be okay for that as long as the fonts don't cause eyestrain. I know I could modify each book to look better, but quite frankly I got tired of doing that.

EDIT: BTW, still no two-column landscape view.