onion.petは安全ですか？

This is a proxy to allow regular web browsers access to "The Dark Web", aka Tor hidden services. As such, it does what it advertises. I can't vouch for any logging they may or may not do; you're potentially giving up some Tor privacy when using a service like this. Just remember: When you browse the Dark Web, you're wandering down very dark alleyways in a very sketchy part of the Internet. Here there be dragons. And worse.