Here's something to keep in mind when evaluating high intensity interval training - HIIT - cardio workouts:
The goal of HIIT cardio routines is to bring your cardiac muscle (your heart) to the point of exhaustion before your skeletal muscles (biceps and triceps for example) reach their point of exhaustion. You know you've reached the point of cardiac and respiratory exhaustion when you're your heart is pounding and you're gasping for breath.
For this reason you should look for routines with exercises that involve a large number or wide array of different skeletal muscles in each movement. This will help ensure that your heart and lungs give up first - before your legs or arms.
A few examples of good choices include:
Take the Burpee - it requires nearly ever major muscle group. Starting from your calves to quads to hamstrings to glutes to hip flexors to abdominals to chest to triceps to shoulders.
Contrast that dumbbell curls and push-ups. Unless you are superhuman it is likely that your biceps or your pectoralis muscles will reach their points of exhaustion long before your heart and lungs do.
Just something to keep in mind when you're looking for your next challenge. If your goal is to really give your heart and your lungs - your cardiorespiratory system - a really great workout, look for these types of exercises.
To help you get started, here is a simple HIIT routine that combines my 4 favorites into one intense session. You can customize this to your ability level by increasing the rest periods or decreasing the number of rounds in each set.
Hopefully, this will help clarify why HIIT cardio is healthy - it makes your heart stronger. If you're doing it right, you should see two significiant results after a while.
Like with any exercise routine, you won't see immediate impact. But that's what HIIT cardio is all about.
If what you really want is to "lose weight" - which actually means to reduce your percent of bodyfat - you probably need to first focus on your diet. What you eat and how much you eat has a vastly larger impact on fat loss and fat gain than exercise.