I remember when Wickr first started on iOS, the founder said at the time that she wanted an app her kids could use safely. I never met anyone who used Wickr though. Pretty good job on their part that it went from a niche app to an Amazon acquisition.
Now that it will have a corporate implementation people should remember that corporately administered clients (e.g. Teams) save and record a copy of everything you say and do and AWS Wickr is likely to be no different.
As Signal is mentioned in this comment thread, I don't see the hit on Signal about the phone number piece as being a big downside. The app is about privacy not anonymity and a phone number is a pretty unique UID. I never installed Signal to talk to anonymous strangers, everyone on my list is someone I know because of the phone number UID. True, I don't know everyone's phone number but I'm probably also not talking to them often or ever.
It's very hard to get people to try a different messenger. People are very wedded to the Facebook corporation (FB, Instagram, Whatsapp). It bothers me when I talk about something and then see ads for it shortly after. Obviously not only is it bot-mined for ad purposes, but rather, I don't believe FB ever deletes the data. They are the administrator and likely keep it forever. This is why I personally think Google is better, they mine it with bots, but unlike FB they don't sell data to third parties.
Signal is probably at the current time the last non-corporate messenger that is secure and is easy enough to setup and use (other suggestions like Matrix have a barrier to entry that is too high because it requires both technical knowledge and the ability to find your correspondents). It can't be acquired due to it being a non-profit foundation so it's likely to be around for a long time to come.