It's the antithesis of self hosting and it's in literally every big thread about self hosting on HN or r/selfhosted or such.
Whether it's to protect from DDoS attacks from some unknown baddies that are out to get you (never happened to me and I host all sorts of crap, including user-uploaded content), to speed up loading in remote parts of the world by 200ms (I tested my site on cloudflare in ~2015 and it didn't work at all, it just literally forwarded every request and waited for a reply), or apparently now to catch downtime somehow (the brand "Cloudflare Tunnel" instead of suggesting an open source caching service running on any old VPS from a friendly vendor near you).
But if you want to be accessible to the outside world, you need to direct your traffic outside; I don't see a substantial difference between routing your traffic through Cloudflare, Comcast, Equinix, or any other major connectivity provider.
And I would mostly agree so long as you're the only one who has access to said data. There will always be "ISPs", of sorts, that your data needs to pass through; that's simply how the internet works.
The nitpick about Cloudflare is that they are starting to act as a gateway to the internet. Maybe you can turn their fronting off if they start giving you trouble, or maybe your registrar also runs behind Cloudflare. Anyway, bit of a philosophical discussion how much power to vest in one company.
The real trouble is that their main offering involves giving them the private keys to your traffic. I don't know if that's also the case with this Tunnel product, but at least for regular websites, then they process your actual data, as with the bank example (a colleague at said bank was not happy).
You would run a program on your system which connects to Cloudflare. The traffic goes to Cloudflare first, and then gets forwarded to your system.
[1] https://blog.cloudflare.com/tunnel-for-everyone/