In my opinion the Vang Comp card is far and away the best on the market:
https://vangcomp.com/shop/vcs-detach...extra-carrier/
The "elastic" is much thicker and more robust than the standard elastic, the "card" part is tough and durable, and even though I beat on mine pretty hard they reliably hold shells rim down (how I prefer to have them) and won't drop shells even if I mag dump as fast as I can on either my 1301s or my 870s.
Plus they are 20 bucks and you can attach them directly to the receiver with some industrial strength velcro.
It's cheap, durable, and reliable. Hard to beat.