Which kettlebells should I buy?

Does Dragondoor offer 3 sizes of kettlebells for us to progress with or can anyone regardless of strength use all 3 sizes? In other words, if I'm already pretty strong should I just get the 72 pounders or should I get them all?

Can a relatively strong person get something from whipping around a 36 pound Kettlebell? If the video will answer these questions I will buy it first before I get the kettle bells.
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