I was with Verizon from my first phone until I first got a smartphone. I switched over to Fi specifically because I didn't want to deal with Verizon's billing, and because I didn't like the company in general.
The low-data approach is really attractive to me -- atm I use less than 500mb a month (sometimes as low as 200-300mb). At that level of usage your prices are very competitive with Fi. My concerns are that I'm starting to migrate away from native services where possible because of the security implications -- more of my texting is happening over Signal rather than SMS, and with the Libre phone theoretically some voice is going to start getting routed over Matrix.
I have no idea what that's going to do to my data usage, I honestly just have to experiment and find out.
Additionally, I'm starting to get more serious about using a VPN everywhere, even on mobile data, since I assume that behind Google, whatever network I'm on is absolutely selling any data that hits their towers. That may drive my data usage up, or it might drive it down because I might feel more comfortable connecting to random wifi networks if I know 100% all of my traffic is going through that VPN.
I'm in an urban area, so this is unrelated to me, but the fact that you're selling dumb phones on your plan is also pretty cool, and I can think of people who would be interested in that if Sprint's rural coverage was better.