What makes a link secret
Two things. The contents are encrypted before they leave your device, so the server that stores them cannot read them. And the link reveals its contents once, so there is nothing to find afterwards. LinkPilot does both: AES-GCM-256 in your browser, the key after the # in the link where browsers never send it, and a burn on first reveal that overwrites the stored ciphertext.
The link itself is the key, which is the one thing to remember. Send it over a channel you trust, and if the recipient reports a burned link before they opened it, treat the contents as exposed.