Bridge mode

My Xfinity service has been very solid, i have lost service (non power related) twice since last July when I signed up. when I do speed tests most of the time i get at least 600/30 meg down/up  (I have gig service). However since both my spouse and I work from home we need service all the time. 

So as an ATT retiree who gets 25% off I will be also getting Uverse. and use it as a backup. my wifi modem supports a secondary WAN port and I can set it up to fail over automatically which is really nice.

I also plan to get static IPs from att (its 15 per month for 5 usuable). Comcast requires business to get static IP and its much more. I am considering changing my modem to Bridge mode. I have the unlimites plan and one wifi SSID that i use for visitors on the Xfinity modem. 

what will I loose if i move to bridge mode?