I bought these on the off chance, just to try them out, as I was buying a new cajon and in the past I have preferred ordinary wire brushes. However they are really brilliant; a fuller, richer, more responsive sound which means I can do more complex fillers etc., and relax more when playing.
They seem to be sturdy enough so far. (I've only had them a few day but I AM giving them a good workout.) And I'm not getting loose wires caught in any clothing, edges etc.. Nor stabbing myself in the hand with twisted, misshapen wires!
If you've not used brushes before on your cajon, go on, get these and have a lot of fun AND increase your range of sounds and versatility. they're not that expensive and make such a difference.
I've had these brushes a good while now and I'm still enjoying using them, AND they still look in all but new condition.