Multiple DNS vendors?

Thanks For recommend DNS, i just curious this safe or not if one DNS have many resolver? Exampe Cloudflare and quad9 have 2 or more resolver if i check on dnsleaktest.

Safe depends on your definition. If you care about availability you probably want multiple. If you want to minimize vendor risk you might want to go with less. You need to put your priorities in order here and make an evaluation for your own situation.