Threema is a pay-to-play client on the App stores ($3 USD on Google Play, €4 on the Apple store), inhibiting it's adoption when the playing field is full of free clients. The inability to try-before-buy (regardless of technical merit) turns away casual users who might give it a shot "just because", myself included. (Theory: the world has been burnt a thousand times over by shitty ad-infested mobile apps and no longer trusts buying before trying. I sure don't.)

And of course, the world has been burned by shitty ad-infested apps because nobody wants to pay for apps... (not that I necessarily disagree with you - I only got Threema because of a trustworthy recommendation)

nod I have had others tell me Threema is good, but it's a "walled garden" until now; Signal has won over hearts and minds by being FOSS and having no cost-based barrier to entry even for casual users. As a FOSS advocate I went with Whisper from the start and recommend Signal to everyone (with a fairly high take rate, non tech worker friends and neighbors) with a simple text link to install and saying something like "it's free and encrypted so nobody can see us talk." (KISS explanation)

(this is a US-centric comment, as phone numbers are rather static here; unlike other countries, not having a number isn't really how it works for most people on the big 4 carriers and their secondary MVNOs)

The world has also been burned by paying for apps that turn out to be actually shitty and-or ad-infested.

48hour refunds on google play should have addressed this conundrum but it seems people just aren't aware of it :(

You can get a refund if you go to the play store and use the refund mechanism within a timeframe.

Technically true and only easy if done within the first 2 hours, after that it's cumbersome (requires a desktop browser to go into order history). I will posit that it takes longer than 48 hours to decide if you want to continue using a chat/messaging app - the dynamics require multiple live humans to interact on their timescales, it's not just playing a game or whatnot on your own.

Yeah, my German-speaking + privacy-minded friends usually have it. I would estimate I can reach about 30% of my German contacts on Threema (if they have any IM at all).

But there's not a single non-German contact on there.