So this is what are known as hopper bellows, and unlike some of the much more expensive options, this one literally just sits between your hopper and your hopper lid, and it works really well!
If you're wondering what the heck are hopper bellows, they're bellows, for hoppers ;-). Ah, you knew that much, OK then ;-), they're for blowing out exchanged retention.
When you first use a grinder (whether it's a standalone grinder or integrated), you'll usually find if you weigh the first dose, a few grams disappear. This is because there are areas inside the grinder where some coffee gets stuck, known as "grind retention".
Some of this retained coffee is what's known as exchanged retention, and this is just a small amount of ground coffee that isn't pushed into your basket by the weight of coffee on top of it, so it stays there until you grind again, at which point this coffee enters your basket first.
This means that you're using a small amount of stale coffee, the first time you grind coffee each day, and you're using a small amount of coffee at a different grind size each time you grind after adjusting the grind.
With Sage machines we're only talking maybe 1.5 grams of exchanged retention, so it's really not a huge deal, but for the best results it's best not to use this retained coffee, and this means purging, in other words, wasting this coffee.
If you don’t do this, it means that roughly 10% of the coffee in your basket is either stale, or is at a different grind size.
Unless, you encourage this coffee out of the grinder at the end of each dose by simply pressing the bellows a few times.
You can get bellows that replace the hopper, which can be a good idea if you want to single dose and/or if you want to recude the height of your grinder, but they’re usually quite a bit more expensive than these.
These are really inexpensive, and they’re very simple, literally just a silicone ring that fit in between the hopper and the lid, and they do the job very well.