I have a lot of experience with them. If you’re thinking of getting one as a cheaper alternative to the sort sold by LH and other sex shop suppliers, think again. A good quality, well made riding crop for eventing or dressage will cost you a lot more than the ones for sale here 
. You might get a kids one cheap but it won’t be long enough, will look cheap and break easily… and for me, would be a bit creepy getting a kids riding riding crop for BDSM use.
On the other hand, if you’re willing to spend a bit more or get a cheaper one that might fall apart, the only ones legal for BS now would be a good intro to whips for this purpose as they’re well made and very padded on the hitting end.
Not relevent to this conversation but this is my review of my horse’s LH purchase because it amused me to write it. Though for it’s original purpose it is now redundant, he has passed it on to his field mate and she is now using it permanently for a different purpose.