All of these products work for different reasons and the different reasons can be very important to what type of product you will use. If you're on a budget you may be able to find a product that works for you.
What is the difference between an interval training program and a traditional training program? I always tell my clients they should start with a basic interval training program for short workouts. These workouts are designed to start and complete quickly with low intensity. The workouts are short and the intensity is low. These basic programs are great to start with as they allow you to build up the strength and power. A more advanced program like HIIT can take your fitness up to a whole new level, but a basic interval program will get you the basic strength and power. It may take a while to get to that next level. I use this basic training program as my base for my programming. The program is not only a way of gaining muscle, but also as a form of exercise for a whole system of fitness.
You can use the exercises in the Basic program in the workout and at the end of the workout when you are done.