Matrix is an incredibly centralized service masquerading as an easily self-hosted distributed service. The moment you try to get a non-technical user connected to a homeserver other than matrix.org, all hell starts to break loose.
It's bad enough that both France (tchap) and Purism have created their own client forks to make on-boarding somewhat tolerable at the expense of really painful rebases against upstream Riot, while Riot tries to get it's shit together on the non-matrix.org user story.
Mattermost has a slightly less painful situation -- they provide a relatively easy to brand/preconfigure client (and fantastic docs on how to do so: https://docs.mattermost.com/mobile/mobile-compile-yourself.h... ), but you lose out on federation and self-service sign-up, leaving your community isolated (sometimes a pro, sometimes a con).
I've personally run 3 homeservers for communities formerly centered around Facebook, only one of which was technical. For the non-technical communities the workflow was the one provided by riot-web when a mobile user visits the homeserver.
Neither of the non-technical communities saw more than 5% adoption in the org. The technical community constantly complained about the login flow.
When I deployed Mattermost with a custom app for the first non-technical community I saw 40% adoption within a week, and 80 within the month. The second community has looked at the first as an example, and I can expect 80%+ adoption within a week or two of deployment.
I've asked repeatedly in both #ios:matrix.org and #android:matrix.org about assistance in putting together docs similar to mattermost's and was completely ignored.
I've asked if the Riot folks would be open to deep-links providing the homeserver to mobile apps, and was shut down by somebody who insisted deferred deep links were the only kind of deep links, and that they would only ever be supported by a Google Play on-boarding flow.
I really want to love Matrix, but y'all make it fucking difficult sometimes.
