I just switched to Insomnia because of a bug in Postman, where it wouldn't pick up changes in the body of an HTTP POST and would use something that had been sent previously. I was able to see that the data received by the server was previous values from the text field. If I cloned the request into a new tab it started working. It happened repeatedly - at some point after making edits to the body it would just get stuck and not send what was in the editor. So I switched because I can't use an app with such issues with its core functionality.

I also disliked Postman's UI, but it wasn't a deal broker. I'm not in love with Insomnia's UI, either, but I like Insomnia because it reliably sends the right request.