With the tube removed, you can have a go at sounding like Miles Davis, but you'll probably have to bend down the lower notes to get them in tune with the higher range, or even the middle of the stave. I guess Miles did too. All practice mutes I've tried have that problem too - including the expensive Yamaha ones.
With the tube in, and fully extended, it actually does play in tune with itself, at least with my trumpet. It still takes the edge off the sound, which makes it less likely to alarm passers by, when I play at home. It doesn't really make it quiet enough to practice with my immediate neighbours at home (I live in a flat/apartment), but that's not what it's designed to do.
You can get quite a range of different sounds out of it, depending on how far out you have the tube, or if you remove it all together. You can also do the Wah Wah effect, by putting your hand over the end of the tube and taking it away, of course.
It's also very shiny, and nice to look at. The pictures don't do it justice.
A good way to get it to stay in the instrument is to breathe into the bell before you put it in. You can also stretch an old ankle sock, with a hole in the heel, over the mute and the bell - yet another sound option :) It definitely won't fall out then. I've read the tube can slide out, or move by itself, and a good cure for that is a smear of cork grease.
