We considered the same tour on NCL a few months ago. Ultimately, we went for one to Sorrento (including lunch at a family farm) and Pompeii. (And, of course, the obligatory cameo factory.) Even that was a very tiring day... yet among the best excursions we've ever taken.
If you're going to pack a lot into one day, consider a ship tour so you won't need to be concerned about multiple schedules. Even with a ship tour, we had a couple of hours to wander around Sorrento, which was nice.
Capri and Sorrento can be done on your own. Adding Pompeii makes it more complicated.