Upgrade my own modem

I am using my own Cisco cable modem with Comcast internet for a while now, at least 10+ years.  Cisco modem is DOCSIS 3.0, handling up to 268 Mbps download speed. I recently upgrade to 600 Mbps download plan and Cisco modem cannot keep up. I plan to replace it with Motorola MB6811 which can handle up to 2 Gbps.

The last time I installed and activated the Cisco modem, it was a less-than-pleasant experience. I had to connect to Comcast tech support on phone, go back-and-forth, configure this and that before the internet was connected correctly. 

For the upcoming modem upgrade, Xfinity FAQ saying that you can activate it yourself. Just install the Xfinity app on your smartphone and follows the instruction. It sounds too good ... So I just want to ask the community if anyone has done upgrade modem yourself and is it a smooth experience. 

Nathan