A simple elastic ankle sleeve works mainly by squeezing the ankle evenly. It can provide a feeling of support and warmth, but it has limited ability to stop sideways movement because the compression is the same in all directions. The Fosta 410cz-3 is different for two reasons: it has a built-in elastic rib that reinforces the sides of the ankle, and it uses a side Velcro closure that lets you change how firmly the support is pulled around the joint.
The rib element is what gives the brace its lateral reinforcement. It is meant to limit excessive side-to-side motion of the ankle, which is the movement people often describe as a feeling of looseness. The Velcro strap then determines how actively that rib presses against the joint. A plain sleeve has no such adjustment; you are limited to the size you bought and the natural stretch of the fabric.
This design places the brace between light compression socks and rigid sport braces. It is suitable when you want a structured, adjustable support that still feels light and flexible. If you need hard immobilisation or a specific angular stop, a stiffer product is likely more appropriate, and a specialist can help you choose.