Xfinity storm-ready wifi and bridge mode misleading and/or confusing marketing

I think the marketing materials for Xfinity Storm-Ready Wi-Fi are vague and/or misleading.  Having used the Unifi version of LTE backup (UniFi LTE Backup - Ubiquiti Store United States), I mistakenly thought this product would work the same - basically just stick it between modem and router, and it'd failover connection from cable to cellular in the event of a network outage.  However, upon receiving, this doesn't seem to be the case at all.  The device doesn't work at all if one is using xFi in bridge mode, and really just works as a standalone Wi-Fi if you're using the xFi Wi-Fi (I'm not, as I already have Unifi).  I'll be returning this, but wanted to post here in case anyone else runs into similar issues.  Hopefully this will save you some trouble.