For 2 lines have had a great experience with them so far my phone started acting up and I contacted them and the guys that answered had me try differwnt things for 3 hours.
I LOVE XFINITY MOBILE!!

We have two mobile phones and share the $12 per GB per gig plan. My wife and I have never come close to exceeding 1GB of data. The process of changing from Verizon to XM was complicated and time-consuming for one of our phones, but it was worth it in the long run. XM shares the Verizon network, which has been excellent in most places other than our home. We also have Xfinity Internet service at home and connect our mobile phones to it by blue tooth when we are at home.

Over all it was decent if you need Verizon coverage for the price. I byop my IPhone XS Max to there network. In places the speed was good and coverage was great, but when i got into really populated places or even when I went to Gatlinburg, TN. The speeds tanked and coverage tanked to the point i was having to swap my phone to CDMA mode to get usable service.

Also worth noting that while on the service in a good area or a bad area. I always had problems with sending and receiving MMS(picture messages)

The support I got from the Xfinity Store was amazing and painless experience.

My average monthly bill of $21 is $15 for LG G8 payment + $6 for data (2 lines using less than 1GB).

Xfinity can be an extremely cheap option for some people. Data is $12/month, but that is across the board, even with multiple lines. With Xfinity's regular phone deals, a family plan becomes very cheap if you don't require a lot of data. Talk and text are free, but the catch is you have to be a current Comcast customer.

For those that need a lot of data, it's $45 for unlimited. In my case it would be $60 with a G8. That's well under half of what Verizon would cost, and Xfinity uses Verizon's network.

You can also BYOD, but it is limited to iPhone's and Galaxy's. They have amazing phone deals though at various times of year, i.e. 50% off monthly payments of LG G8, $200-$300 off Pixel, Galaxy, iPhone, etc.

I haven't had much experience with support, so I can't reliably comment on that. Overall I am loving Xfinity Mobile so far.