These small mutes are ideal if you are practising in a flat, or a small space, such as a Naval vessel! Practising without them is the ideal, but this is the real world, and some practise is better than none!
They can reduce the volume of the saxophone by 50%, and the simple instructions are easy to follow. You might find that there is more resistance than you are used to, but this is easily fixed by experimenting with some softer reeds.
A perfect solution to small practice spaces.