I've chosen to pay an extra $0.50 or so per domain to Porkbun for the option of using other nameservers.
I've also had a billing issue with Cloudflare Registrar. I transferred two domains and paid the renewal fee, and two months later was charged for the same domains again. They've since issued a refund after I raised a support ticket (still waiting on that to hit my card), but the fact that it happened at all is worrying to me.
Granted I was in early access so I expected some things not to be polished yet, but these are pretty critical areas to get right as a registrar. And since my billing issue happened just last week I doubt that issue has been fixed with the general release.
So I'm going to hold off on transferring more domains until it matures, or just stick with Gandi.
There's several other features I find missing compared to a more mature registrar, but hopefully they'll get there eventually. For now, I'm moving my low-importance domains over to it for the cost savings, but will keep my primary domains under GoDaddy.