I've used TOG 3 & 4 so far - these are the classic versions, not redesigned.
How easy TOG is to use depends on how many you are schooling, what levels, and your goals. I am schooling 4 right now - rhetoric, dialectic, upper grammar, lower grammar (these are TOG distinctions - they're a bit different from WTM) - and without TOG I would be LOST.
Yes, there is teacher prep. I'm a former SL'er - and I miss those days, but I also had fewer to teach. SL only worked for me when I had 1, but I'm glad I have books. TOG teacher prep gets MUCH easier after the predicted "four-week fog". The reason it looks so complicated - let's face it - all of the materials for all the levels is a LOT to wade through. Once you know what you're looking for and how the flow of your week goes, it all clicks into place.
No, TOG is not GB heavy. Yes, they do read enough to get a feel. And yes, especially in lower levels, TOG is heavily historical fiction (much like SL) and for me, that is a terrific draw. I would say, from my limited experience, that TOG lit for high school is more of a "standard works" approach. Twentieth Century lit has included Ivan Denisovich (Solzhenitsyn), The Chosen (Chaim Potok), The Glass Menagerie (Williams), and the like.
Hope this post doesn't run on. I don't post much, but had a couple of moments and thought I'd chime in!