Dumbbells in a workout are great if you are trying to target specific muscle groups.
They are great at shaping the shoulders and upper back and these are my main focus when using them.
Using dumbbells allows you to isolate muscles easier and also identify weaknesses in your left and right sides.
I also use them for compound movements (where you are using the whole body) such as a squat to press.

Kettlebells are a really challenging workout and can be used to really improve overall strength and core strength.
I have had some fantastic results with kettlebells and so have all my clients. They are one of my go-to pieces of kit and I love to use them in a lot of my own training.
Kettlebells are extremely versatile and you can move and improve all planes of movement with them.
I advise you start with a light kettlebell (6-8kg), if you have never used one before.

High Intensity Interval Training is doing one exercise for short bursts and having small rests in between. The idea of HIIT it that the intensity is so high throughout that you only need to do 30 minutes of it! You are working in your aerobic & anaerobic zones which helps to speed up your metabolism and also improve your cardio and lactic thresholds. We use HIIT for most of our classes and incorporate different elements in each class.