Is blockfi safe?

Convenience wise. Probably not as you'll need to transfer somewhere to withdraw to SGD. If you want something convenient and safe, you could use Gemini, the interest isn't as great but it's MAS regulated and you can withdraw to your SG bank account using FAST within like 15 minutes. If you haven't signed up for an account on Gemini, you can use my referral link in my bio and we'll both get $10 in Bitcoin after you make a $100USD transaction. :)