Psst. Unlimited 45-day ZBrush trial this way ->
https://pixologic.com/zbrush/trial/. I'm told you can make a different email and basically have the trial indefinitely, if you're so inclined.
As for usability, ZBrush is a giant pain in the arse to learn, unlike Mudbox (from what I hear, I've never used the latter). The UI is unlike anything you see in other 3D tools, and you have to go through some seemingly meaningless motions in the course of regular workflows.
That said, it's extremely functional and useful once you get accustomed to it. Automated remeshing, alphas, ZModeler, the list stretches to the horizon. I'd argue that, if you have a tablet and lots of time (and/or enthusiasm), ZBrush is well worth your while to learn. It depends on how much you want to do sculpting versus low-poly, of course.