I put myself and my parents on Xfinity a little over 5 years ago. I followed the advice of the community experts on the Xfinity forum and bought my own modem/router. It’s not just for the money savings (about $650 so far) but also for compatibility and control. It’s not just Rokus that have issues but other streaming gizmos, doorbells, thermostats, crypto miners, security systems, locks, gaming systems etc. (I don’t think you can even select your own DNS on some Xfinity routers.)
My parents on the other hand have been thinking pretty short-term since turning 90 and rented theirs. Though in hindsight they would have obviously saved going the other way too. But I was happy to let them make their choice thinking I wouldn’t be responsible for a device that I hadn’t convinced them to buy. (Hah! That didn’t work!)
Fortunately, their wi-fi needs are very modest (they don’t know about this streaming thingy) but I still have to go over and mess with their router when Xfinity knocks their printer off-line.
It is pretty amazing that people complain about contacting Xfinity too, in spite of the fact that the one-time purchase price of a Roku Express is about what a typical person pays Xfinity each week.