“Anonymous”, “encrypted” and “temporary” describe different things. A service that does not ask you to create an account may still process connection information or retain logs.
Ask what is actually protected
Transport encryption is not the same as end-to-end encryption. A disappearing message interface does not prove that backups or server records are deleted. The other participant may also capture a conversation.
Check the service documentation
Look for a privacy notice that explains what is collected, how long it is retained and who operates the service. If those details are not available, do not assume a promise of complete anonymity.
Correction to this page
The previous text made absolute claims that Veil kept no logs, backups or conversation records. Those guarantees were not supported by a technical audit here and have been removed. Do not share sensitive information on the strength of a promotional description.