It’s not an arm band, but I use OPSITE FLEXIFIX adhesive surgical tape to help keep the Libre secure.
It works well for me. However it takes a little practice to apply the tape with one hand.
I also use hemostats for removing Libre and infusion sets. My fingers are to big to easily lift up the edge of the tape. The narrow ended clamps can easily capture the edge of the adhesive disks without grabbing a chunk of skin.