It does what it claims. Although the quality of the finishing a bit inferior with sharp edges here and there. When you're paying 15 Euro for a piece of plastic, you expect it to have a better finishing. Apart from that it didn't fit properly in the lead pipe so I had to use extra filler material for a tight fit. Although it says in the manual you might have to use pvc tape for a better fit, nevertheless the whole process is annoying. For trumpet, I found that back pressure equals to the instrument when the dial is pushed to the lowest position leaving all the hole open, not while 'parked' covering the bottom perforations as it says in the manual.