“When you use Signal, your data is stored in encrypted form on your devices. The only information that is stored on the Signal servers for each account is the phone number you registered with, the date and time you joined the service, and the date you last logged on.”
I use Signal as my main messenger and it works just fine. The only drawback is phone number requirement, but it is simpler for casual users. I’d really want them to add an alternative, more secure and private signup method.