Cloudflare works really well and has a good UI. Namecheap also works well, but it takes more clicks to adjust DNS records.

I have not, but from screenshots it seems only a minor reskin.

There was a Linux client I saw a while ago—Spring Mail or something like that?—which first downloaded your email from your provider onto their own servers, then your local client got them from their server. This additional cloud step is what I want to avoid.