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.
I can't really speak for its security. Afaik the protocol is almost considered stable, and I trust it for everyday communications — but I wouldn't trust it if dealing with a nation-state level adversary.
The only privacy pain point is that if you run a synapse home server (the reference implementation), by default your voice and video chats are routed through Google's servers. You have to run your own TURN server alongside synapse to prevent this. This is fine, but imho it's not well explained on the install guide.
Riot is... Okay. It's great ffor power users, but imho is quite obscure for the average chat app user; the ux isn't great yet. Perhaps with the redesign...
Lastly, bridges are the biggest reason why I want matrix to succeed... But as of now, none of them are really useful or even usable. They're all in very early stages of development and need contributions.
Why do you say that? I know many projects using bridges successfully. For example the UBports [0] guys have bridges between their Telegram and Matrix rooms.
Besides FluffyChat [1] works wonderfully on UT phones, so that's a plus for them.
[0] https://ubports.com/ [1] https://christianpauly.github.io/fluffychat/
I use it daily to communicate with three of my friends in a group chat. I use Riot on iOS, they use Riot on Android.
After the initial setup, I haven't had a single issue with it to be honest.
On a somewhat related note, it's hard to get people to switch to something new, but I was able to get my non-techie friends to switch by showing that we can use it to exchange high quality videos without any size limit (well, I actually have it set to 1 GiB, but I can change it). That's one of the biggest issues when communicating between Android and iOS. Sending videos over MMS sucks.
As far as I saw you can also bridge to other messaging services, even to WhatsApp [1] which is why it might be worth a try.
[0] https://matrix.org/blog/home/ [1] https://github.com/tulir/mautrix-whatsapp