"hardly has drawbacks" My notes on Signal contain the following:

+ It usually just works

+ Reasonable desktop experience (needs to re-link once a month or so, but otherwise independent and not terrible UX), good mobile experience

- Metadata handled by Amazon

- Phone number is a hard requirement, and changing your phone number means re-connecting to everyone

- Funding comes from Facebook from what I recall, and even with large amounts of their $100M invested, their expenses are 8 times larger than their income.

+ At least it's a foundation and their finances are not a black box!

~ With a build from an untrusted third party, you can make it work on Androids where Google Play Services are intentionally firewalled off.

~ No audit of the clients. The protocol, sure, but most bugs aren't introduced on a protocol level.

These are only things they could solve, i.e. that others do better. That their contact discovery solution (where you upload your phone book) is broken isn't a downside because nobody else has that figured out either.