I love TOG for my multi-aged family and we have gotten a lot out of it!
What I found for the high school years was what someone else mentioned before. I would end up spending too much time planning for all the levels instead of using my time to read the higher level books. So, I opted out of TOG for high school and went to Omnibus I.
Now, I do use TOG for elementary and middle school because I haven't found anything better out there and we're on a roll.:auto:
Now, my highschooler will get his history credits done in three years with the Omnibus, instead of four and he will have the fourth year to pursue something of his interest such as more history :glare:, philosophy, or something else.