I have climbed on both the zz and the sj3. Both are great devices.
I recommend the zz to most people because it’s intuitive, can crossover to single line work, and is more affordable. I personally climb on the sj3, and absolutely love it. It takes some dedication to developing technique with it, but once you do, you can climb blazingly fast, with little fatigue (with a pulley up top). The fact that you can lock it in place is really valuable; you can perform tail-over redirects really quickly, or lock off before a really dynamic event. Between the two devices, the control of decent speed is greater with the sj3, making inertia swings easier. It’s also easy to over-do without practice. I have seen inexperienced users take uncontrolled descents when attempting complicated maneuvers. On the other hand, I have seen people take uncontrolled descents with the zz when the mechanism was unintentionally pushed down by knots, branches, elbows, etc.
Another detractor to the sj3 (besides the learning curve) is that it takes maintenance. The zz is relatively maintenance free.
As you can see, there is a decent amount of give and take with both devices. Both are better than a hitch, any day.