You can use public key fingerprints to ensure that you are connecting to the intended SSH server even on first connect.
Planio currently uses keys with these fingerprints (in hexadecimal format):
77:d1:54:d7:33:7e:38:43:40:70:ca:2d:3a:24:05:22 (RSA)
When using OpenSSH 6.8 or newer, the fingerprints are shown as a SHA256 hash (in base64 format):
SHA256:OCkTD3x0ZyLFpqaVtLjg7z3gnocCWP83LIs0Wu1zXYE (RSA)