Is Xfi Gateway the way to go?

I've used my own modem and dedicated linksys router for my internet at home through Xfinity.  They are both at least 4 to 5 years old now I believe.  I've always notice on my 200Mbps plan, that my download speeds are rarely over 10Mbps.  I assume my older equipment is partially to blame.  However, I've never had problem online gaming (or maybe I don't know what I'm really missing).  We did also cut the cord to satellite TV this month and I noticed our data usage is near the 1.2TB cap this month which is first for us.

Xfninity support suggested the Xfi Complete plan to avoid overages, with their Xfi Gateway modem/router.  If I upgrade to this, will my speeds most likely increase significantly higher than 10Mbps?  Upon disconnected my current router and modem, is installation pretty much simple?  I'd hate to get it and run into connection issues right before the holidays and not be able to stream or use the internet.  Do devices such as Xbox One, Roku streaming sticks, phones, etc. find and connect to the Gateway once set up with ease?  Thank you in advance!