Hi! I did the VIP Tour (not private, as there were only two of us) last October with a friend. I'd highly recommend it! I'm not a huge Universal fan (I'm holding a grudge over Jaws, which was my favorite ride anywhere when I was 10), but the tour was a fantastic experience that I would say is absolutely worth the money. We were able to do nearly all of both parks in one day, and our tour guide was great. We saw some fun behind the scenes things, jumped to the actual front of every line, and really bonded with our tour-mates! As a Disney for life kind of gal, it gave me a Universal experience that I will also treasure as a memory.
I'd offer two minor "warnings" about it, since you're working on a decision. First, as someone with a lot of food allergies/dietary restrictions, I found the lunch that was included to be problematic. At Disney, I am used to converting a quick service credit to two snacks with some regularity, but this was not an option. I had GREAT tour-mates though, and they were happy to trade me a snack for a meal. This is probably a rare problem to come up against, but I do feel it is worth mentioning. The other thing I'd keep in mind is that with a great tour guide, the tour can go as late as 6pm. The day we were there, the parks closed at 7, so we didn't really have time to do much that wasn't a part of the tour. This is a pretty minor drawback, in my opinion, because there is very little that isn't included on the tour, but if you were hoping to spend time in, say, the Dr. Seuss area, or see some of the shows, I'd recommend choosing a day with longer hours!
I don't think you'd go wrong with the tour. In fact, it's probably the only way I'll do Universal going forward! (like I said, I'm not the BIGGEST fan, but I was definitely pleasantly surprised!)