If you want a good supplement, go with Creatine. It helps reduce your recovery time and increase muscle deposition. I use it all the time, as do hundreds of thousands, if not millions, of gym-goers across America and Europe. I recommend Body Fortress or Six Star, but most brands are good.
As for HIIT, it's great if you do it right. From what I've heard, read, seen, and experienced, it's better than just running at the same pace for the same amount of time. It seems to be better for fat-loss, but it has good cardio benefits as well.
If you're referring to the Turbulence Training For Fat Loss book, it combines both cardio and weights, so it's a bit different than HIIT; however, it does seem to be effective from what I've seen. It all really depends on your body and what your goals are. Because it combines exercise and weight-training, I'd go with Turbulence simply because the addition of weight-training will enhance your results; however, if you're on a tight budget and can't afford the book, go with the free HIIT resources online until you can afford it.