Same product as the one that comes directly from the manufacturer. Saves me a lot of material when working with different size flasks. I can also shuffle them around so they hold various size tube racks as well by fitting around the corners. Note: you need the magnetic base to use these!

But who can complain about that? You don't want your sample to fly off, right?
Seriously it's pretty strong. My shaker has a rubber mat, so if I place the mat between the magnet and the platform it works great.