anyone had luck with these fly-by night cell carriers?

I see ads all the time for shit like consumer Cellular, mint mobile, stuff that rents time on Verizon towers and sells you a plan for like half the price.

I'm trying real hard to de-Xfinity myself but the cellular plan is the cheapest of all the major companies. Yes, I know they also piggyback off the Verizon network, but at least they have 24/7 support