Thanks for the feedback! I actually released an update 0.3.6 earlier today that addressed some issues with compact mode and the alternative mobile UI. Especially the thumbnails should look a lot better now.
Regarding the thumbnails, they didn't actually use more vertical space than in the standard UI as they merely used all the available vertical space. The issue was that since the whole element is larger because of the thicker footer, the background got stretched out to fill out the additional space, resulting in the portrait format you are talking about. That should however be fixed now, but if you prefer the smaller standard UI, that sadly won't help you in this case. I guess that's what makes it an experimental UI :P
Regarding the comment box, I agree completely and before I repacked my scripts into the KUP bundle I did actually have a fix for that. I never included it in KUP though since that feature is already included in the excellent Kbin Enhancement Script plus a number of other improvements. KUP is fully compatible with KES so I felt I should rather focus on bringing new improvements than reimplementing things that others have already solved.
If I get some time over, I might add that however, in order to make KUP more of a complete single package.