Setup was smooth, server operation is transparent, user management trivial and everything just clicked into place when we were looking for a simple yet functional solution to team chat

Mattermost was absolutely trivial to set up and maintain, which was a huge plus back during the first dawn of Covid where we struggled to find a solution to team chat that allowed us to host on-premise, keeping all our data local - a must for many projects which have complicated data privacy regulations that are a nightmare to work around with cloud based products

One of the paid feature is unlimited search, and as a free user (10,000 line search limit, I think), it is often unclear whether you can't find what you're looking for because you hit the limit or because it's just not there.

Mattermost allows us to quickly keep connected to our colleagues across the world. It allows people to form groups and chat easily to many different teams, all within the same desktop app, web app, or mobile app.

This software is very easy to install and supports a simple Docker install, which makes it easy to keep up to date and secure. There are multiple examples on installing and running Mattermost in different cloud hosting environments, and the user community is also very helpful. Running the software locally means you can keep a much better eye on its security and usage. Its user management and directory integration is superior to Slack's. The desktop and mobile clients are fast and easy to install/configure/maintain.

There's not much that I dislike about Mattermost. Its open source nature may put some people off, but paid support and enterprise licensing solve that issue immediately.

Slack with AD integration at half the cost. But I still wish I could afford Slack.

Slack integrations just work on Mattermost. The theme choices are very nice. The ability to host my own on-premises server is very nice. Technical support staff is very knowledgeable and competent. I'm not made to feel like an idiot if there is some specialized knowledge that I don't have.

The Android client is extremely buggy and fairly slow still. Selecting a push notice to open Mattermost to view and respond in the thread does not always open the right thread and is always slow (even on LAN, with the latest gen of Android phone!)). The client MUST be snappy and it just.. isn't. The Windows client becomes slower and slower the longer you have it open, so it must be restarted every day or two. It's a little buggy; sometimes new messages make your view scroll up instead of down. But it works well enough most of the time.

We moved a large team of users in a very short time. Since we only need the communicator 99% of the time for communication between users, we reduced the cost of paying for another tool by 96%. With a similar look and functionality to other instant messengers, the transition was quick and painless. The team very quickly implemented and accepted the new tool.

Convenience of installation, practically free for most users, quick and easy implementation, very similar in appearance and functionality to top messengers, so it is very easy to move even a large group of users. Works fast and does not consume a lot of memory. Lots of add-ons and plug-ins being developed.

A few UX issues, but not significantly affecting the user experience. For example: No ability to search for users directly from the search bar, no preview of more than 1 image file, no internal media player, linking to YouTube instead of playing right away.