At the time of this writing, macOS Sierra and iOS 10 are both available as public beta 1. I’m using Sierra on 2 different laptops and I’m using iOS 10 on my iPhone 6+. I like most of the new features, but boy are these releases rough! I’ve used Apple’s public betas for OS X before and I’ve used the developer betas for iOS before, but these are the most unstable and performance challenged betas I’ve seen yet.
Sierra runs noticeably better on the newer of the two laptops (a 2014 MacBook). On this one, performance problems remain and app crashes are common, but at least the computer itself stays running. On the older of the two, however (2012 Retina MacBook Pro) this thing is a nightmare. The entire OS crashes after every couple of hours of use. If you let it sit for any length of time, it will likely crash when you come back to it. Sometime it won’t even boot successfully. Even when it does boot, browsers fail to load the Flash plugin frequently, Siri won’t open, you get the picture.
I would highly recommend waiting until things get a little more polished and hold out for at least the next version of the public beta. Just my two cents.