That said, I wouldn't last 8.4 months like the author. Even though he admits to some Google app usage, I'm in too deep — I'd never be able to get out. But if I get the chance, I'd like to try it on a secondary phone. Those solid black icons are one reason. They look cool.
I personally just encourage people to take a look at what you are using, and if you could gradually change some of it. Who knows sometimes alternatives even offer better services. I am not saying never use anything google ever again. Just question your tools regularly and peruse the alternatives.
I'll also echo the ideas from everyone else here. You can just use it as a normal Android phone the way you do any other and there's still big benefits. There's also really big benefits in terms of carrier privacy that aren't often talked about, like vpn routing and hotspot usage.
Running Graphene for a long time now, everything works perfectly fine, but I don't do mobile banking.
I also work in mobile app/SDK publishing as a business dev and it's critical that I can install my clients' apps (thousand+) in private space.
It works great for me.
also you can restrict some apps network permissions, for example i use the google camera app with the network disabled :p