Personally I care about the security of the server (is it written in a language that historically has a good or poor track record), and I care a great deal about the client.
The Slack client regularly pauses for me while I am typing, randomly refreshes, and generally feels sluggish. Those aren't things I associate with Go. That said, I think this particular implementation's client is also written in Javascript, so I don't know that it will have a particular advantage there. But an open source implementation at least won't block alternative clients (e.g. https://www.kickstarter.com/projects/2137936555/taut-the-fas...), in a way that the Slack Terms of Service would seem to do.
The desktop clients are built on Electron [1]. I've been using it for about 3 weeks and there's been a few times where performance issues were noticeable but not bad enough for me to start digging in the code to find the issue. Overall I think it's a well put together app, but people who hate anything built on Electron will probably have bad things to say about it.
Slack's performance also depends a ton on how much your teams are using it, and how many teams you're on.
"reactjis" are one of the worst offenders -- I've had a channel open with some people messing around with them, and it'll be casually consuming 30% of cpu and 3 gigs of ram on my top-of-the-line macbook.
I would have long since deleted an IRC client that was such a poor performer, but unfortunately there's not any good/complete 3rd party slack clients.
Lots of poorly written webapps give Electron a bad name. Slack, unfortunately does have it's performance issues, but there are other popular chat apps written in Electron that are very performant, even on large teams.
Hey - i made that kickstarter! Unfortunately it doesn't seem there was much interest so it went nowhere. I still think it's regrettable how resource-hungry the official client is, but doesn't seem that too many people share that opinion.
The Slack client regularly pauses for me while I am typing, randomly refreshes, and generally feels sluggish. Those aren't things I associate with Go. That said, I think this particular implementation's client is also written in Javascript, so I don't know that it will have a particular advantage there. But an open source implementation at least won't block alternative clients (e.g. https://www.kickstarter.com/projects/2137936555/taut-the-fas...), in a way that the Slack Terms of Service would seem to do.