I mean, people use it, it's not terrible, I just found it unreliable since at the end of the day it's a PHP app. Though Horde (which is also PHP) was miles better. I think z-push uses the php imap library, which is quite ineffecient. See https://wiki.horde.org/activesync#toc29

SOGo being written in obj-c means it's fundamentally much better suited to this task.