Is it compatible with Fully Ajaxed popup login?

As the author of this plugin, I have no idea. I haven’t used that plugin. Did it work for you?

Will this plugin adds or changes mySQL database?

The CDN part of it will add a few blog options, that’s all.

I read some negative reviews I really scare of the conflict and break down website even deleted it.

Is Cloudflare more safety than WP Super Cache?
Is WP Super Cache faster than Cloudflare?

Please advise. Thanks in advance!

There are 2m active installs of the plugin. It’s very stable but occasionally people run into problems.

Cloudflare is a third party website you would have to sign up on, and while it’s unlikely to, it might go out of business, or suffer a breach that takes the site down. Unlikely I know but you asked.

Probably not. Cloudflare use CDN servers all over the world so they can serve content from a server close to you.

However, there are trade offs. You’ll have to search for documentation and reviews of Cloudflare.

No questions your support is much better. Let me study more further from both. Thank you Sir.