It's by and large the slowest, jankiest, laggiest software I use regularly. And I say that as someone who swears Adobe has added a bunch of sleeps in Lightroom.

On basic chat: it will sometimes scroll up when I get a new message, while I'm actively participating in that chat, so I need to scroll back down to read the new messages. Occasionally it flickers, for bonus points. It will not mark the chat as read if I'm on it without clicking on a different chat and coming back. It's the only software I use that, for some reason, has an effect on my typing accuracy. Don't even get me started on its handling of copy/paste. I'm also pretty sure there's some joke I just don't get around the search function.

For calls: it refuses to pick the correct microphone, and will sometimes mute it completely somehow (I lose the feedback in the headphones – I have a jabra headset that does this). This will even happen when I hang up a call and start another one right away. Other times it works well. My default mic is always my wired, always connected, headset mic. I don't use BT headsets that switch from music to communications or whatever depending on what I do, which could confuse the available / selected mics.

It drains my laptop's and iphone's battery like no tomorrow, even if I turn off video and only do voice chat, even if nobody has the camera on or shares a screen. Also, on Windows, for some reason it doesn't use the native notifications, but implements its own crappy ones – but this isn't that big of an issue, since I mostly disable them anyway.

All this is happening on both the "heavy" (heh) Windows client, and on chrome on Linux, both running on a fairly beefy new PC with gobs of RAM. Fun fact: the experience was exactly the same on my 5-year-old laptop with a U-series Intel CPU, so I don't think it's a resources problem.