This is another aspect of inter-portability that, I think, is often ignored. Matrix is doing great on this front. But then there's another concern here, which any Matrix/Riot user would have noticed - you interaction is as secure and private as the least secure of the two (or more for groups) clients in conversation - unless of course you enforce encryption which is also something you can do in a Matrix client. But it's nowhere near the WhatsApps and Telegrams when it comes to user of use.