USB tethering with Franklin T10 hotspot

I started a new line with a Franklin T10 hotspot. My plan was to use it as a backup internet connection for the house, since I work from home and my ISP is less than stable. I'd like to set up the dual WAN function on the router and just leave the device plugged in to the USB port.

The device works great for wifi (mifi) usage, but I cannot get USB tethering to work. I've made sure the USB option is enabled in the settings, and I've tried plugging it into Windows and Mac laptops, and directly into the router.

Anyone else found success using USB tethering with this device?