I would recommend trying it anyway. The really poor reviews are from 5-8 years ago when it was legitimately difficult to use. They recently rolled out an overhaul that's significantly improved.

We used Zulip at a company I was at (about a decade ago) and everyone on the engineering team refused to switch from it to Slack, even when it looked like Dropbox might end the product because it was so loved (it's completely independent now so that's not been a concern for a long time).

At my work we use Zulip, and I haven't really found many people complaining about it. At least on iOS works just fine for me.

We found worse mobile apps was good because it put boundaries around our interactions and kept us using it in a focused way during work hours.

The Zulip app is just fine, at least on Android.