I bought these brushes to use with my Cajon, as the brushes are made from nylon and don't damage the plywood surface of the Cajon.
Construction:
They have a rubber coated handle that is large, comfortable to grip and pleasant to hold. The striking part of the brush has nylon bristles that are thick but flexible and seem very strong. I don't have any worries and they look like they'll last a long time.
Flexibility and sound:
I love these because they're flexible. They have two rubber rings surrounding the nylon bristles. The rubber rings can be moved low down near the handle, allowing you to get a 'swish' type sound. If you move the rubber rings higher up, they push the nylon bristles closer together and allow you to get a solid stick sound.