Spectrum uses Verizon's network. I switched from Verizon to Spectrum last year and I'm saving about $100 a month. The only downside is if the network is busy, Verizon customers are first. So far, I've never noticed a slowdown.
Spectrum has their own secure Wi-Fi network all over the place. Often I'll look down at my phone and instead of being connected to 5G, I'm connected to Wi-Fi instead.