I'm a total alto saxophone beginner, so take my review with a grain of sault. I didn't know before I bought my alto saxophone how loud it was. I'm a guitar player for 25+ years, and I never had an issue practicing in my home studio. Once I got my alto saxophone, that was no longer possible, as I would disturb the neighbors, my wife and kid.
In short, this mute changes that completely, and I could not image how much stagnation would one go through if you couldn't practice at home.
Some youtube videos claim that this item is expensive, that it's not needed for beginners, etc. I cannot disagree more. The most expensive thing for you as a musician, especially a beginner, is not practicing. That will demoralize you, you will not make progress, and even worse case, quit.
All in all, you must have this, it's amazing.