A few users have mentioned that the handle will flex if you pull focus fast.

This is indeed intentionally, as we believe it is a great help to prevent camera shake – particularly when you approach an end stop.  However you can always choose to grab it further away from the end in order to reduce the flex. You can even grab the Ruler as a steering wheel if you have a solid stable tripod or if you e.g. are using a shoulder rig.

But if you operate the handle gently from the end – you can pull the smoothest focus from almost any flimsy tripod…