I've been using Matrix with Riot since 2016 (then called Vector). Rooms aren't encrypted by default, however you can turn it on with the toggle of a button. One drawback I've noticed is Riot uses a lot of battery on Android (this is probably due to me not using the GCM back end), and on Linux as well (this is probably due to it being an electron app). Sadly there is no other Matrix client which is as featureful as Riot (for example, most of the others don't have E2E support), and so we're kinda stuck with it.

I also tried setting up a matrix home server with synapse, however I couldn't get it to work with an nginx reverse proxy and let's encrypt, and decided to just settle with using the default home server with E2E enabled. Others have had more success with this however, so I must be doing something wrong.

The experience is pretty good, and my friends and I have tried the Slack, IRC and Telegram bridges and they seem to work pretty well (infact the telegram bridge was so fast that I thought my friend was using the native client when he was messaging me). Haven't tried WhatsApp yet, though.

I've also used matrix and riot to connect to large group chats on IRC and Matrix and overall its a more pleasant and user friendly experience than using IRC, especially on mobile.