I've been working out with HIIT training and weights since i started. A lot of people always think how 45 minutes a day can be any effective when getting fit. Well the answer is even more effective than a conventional gym workout. Some people spend hours at the gym, doing conventional machines, combining with cardio. That's good, it is also effective. BUT I love to work with kettebells, you can activate your muscles in so many kind of ways. You can be doing a whole body exercise that targets, core, legs, gluts, arms and even lower back. It's definitely not the same carrying a 100lb on a machine that on a KB. How your body need to be engage as a whole it's amazing. You can work at the same time strength and cardio. That's why it's called HIIT training, because you work an amazing amount of intensity in intervals of time.
This also, which also a BIG WIN for HIIT training, has to be done without long time of rest. When you do this, you start creating resistance, something that working with conventional gym machines can't be done. Being at a "conventional" gym can give you the time to do your workouts at your own time and rhythm, if you want to rest after doing an amount of sets, you do it. I'm not saying going to a conventional gym won't workout but if you ask me, I've been all about HIIT trainings for the past 5 years and the results are amazing, my resistance and strength is just improving every year.