Scraper tubes, I would not be interested in, as clips get deleted from there, and there is also duplicate titles issue, and it sounds like a lot of mess. I've seen a network of embed tubes, and they were not getting too much traffic. On the other hand
video-one.com is an embed too, and it is like #34 adult website, in the World. Again, I have not worked on tubes yet. I would get like 1,000 top tubes by Alexa Rank, and could be 1,000 by SemRush Rank, and look at them through something like Similar Web, see where they get their traffic from, and how things work.
Tubes dont seem to be very good for seo, as it is not easy to add keywords to these sites. You pretty much add videos, and describe them, and like you said, it could be an every day work. To me, this sounds like buying traffic, trying to break even with income from ads, watching these videos, in order to describe them, and in general like not the best path to take, but I am not sure. On the other hand tubes should not be bad for seo, as this is what ranks for a lot of xxx keywords, but I am not sure. Tubes does not sound like something for me, at this point.
Mid level tubes sounds like something good, something like Bravo Media Group, but again, this takes a lot of every day work.
Fooxy.com seems to be good too, by the way, I just looked at their stats. I think that DansMovies.com and Fooxy.com people have somethig to do with dlxer.com, but I am not sure, or people from Smart Scripts. DansMovies.com and Fooxy.com are long time "icons" of online porn.