I would actually prefer subtitles about half the font size of what is commonly used - I like smaller subtitles, I can read them more quickly with less eye movement. But a proper black outline or shadow on the text needs to be there too, for good readability.
I watch them on both - Blu-rays on the big screen, and streaming on one of my 27" monitors or on the 52" TV in the living room. For both the projection screen and the monitor I sit at a 1:1 viewing ratio (screen width to distance), but for the TV in the living room I'm usually sitting at the far side of my kitchen table, on the other side of a 3' high dividing wall/peninsula, so there I'm about 15 feet from the screen. That would be the only instance where the smaller subtitles may be a bit of an issue.
I had to increase the subtitle size on Amazon, it wasn’t that I couldn’t read them (though I read far too many websites at 100% scaling in 4k, that’s probably not doing my eyes any good...) but I just felt the smaller subs drew my eyes towards a very specific part of the screen and distracted me too much from the picture. I sit about 40-60cm from my screen dependant on whether I’m leaning back in my chair or not, I’m afraid I wouldn’t know what a viewing ratio was if I saw one.
Guess the ones with the storage box are actually the same boxes for season 1 and season 2, to actually house both seasons in the box. Didn't find anymore about this myself, but hey maybe someone has more info about this.
Either way this is very tempting to get, especially since we probably will not see a UK release for season 2.