I tried out all the 10" files on my netbook and the most readable was the 12pt landscape in two columns, which I kept
The two-column layout works well for the numbered lists that make up the bulk of the text, but it's a bit laborious for the larger blocks of text in the introduction. I might have done a single offset column half again as wide as your split-page columns for the introduction only.
While I generally find portrait preferable, in these portrait editions I found the lines too long for comfortable scanning. While I appreciate the effort to put my screen real-estate to use, half-inch or one inch margins might produce a more readable text.
I do like the presentation of the main text in the landscape copy, and will keep it on hand for reference. On brief perusal, the translation seems more accessible than my print edition.