“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.”
All fair complaints. I’ve managed to switch over all of my contacts to Signal (that I care to talk to, at least).
My biggest gripe is no back up support on iOS, meaning that if I lose my phone I lose everything. People have tried hand waving it away as a privacy feature, but I think backing up messages is a bare minimum for a messaging app - especially with the released of Advanced Data Protection for iCloud.