I bought these because I was playing percussion in a production of Miss Saigon. As I am not a percussion player (My main instrument is tuba) I used them to practice all the tuned parts. They are worth buying for quiet practice, but are not loud enough for a performance.
They are built very well, I didn't do any damage to them over a month of playing, and I have used them on an orchestral bass drum and cymbals. The only problem I had while using them on the xylophone was that a white powder started to come out of them and leave marks on the instrument. The marks where easily wiped off, but it's still a bit odd!
I never got to try them on a tambourine, but I'm sure they would do the job.
Overall, well worth buying for any percussionist as they are very versatile.