I have. I'd prefer the Gear S3 but it is too big on my wrist. Both Gear S2 and S3 classics are far better looking than the Apple Watch (imo). And I like that Tizen allows a keyboard input as well (numpad keyboard with alphabet support, like mobile phone keyboards back in the day). I think its better than handwriting recognition (aka Scribble).
Unfortunately, you cannot reply to notifications from the S2 if you are using an iPhone. This was a major deal breaker for me. And the Galaxy S8 is downright gorgeous... really wanted to switch over. Nonetheless, I'm still sticking with iPhones only because of the Apple Ecosystem. I love how seamlessly my devices work/sync together (iMac, MacBook, iPad, iPhone) such that I can just take any device, or the best device for a task, and start working. I love how I have access to all my files on my phone easily at any time too. I pay for iCloud storage for this convenience, but I also do use OneDrive, but the latter is not seamless.
If not for the ecosystem, I'd pick the Samsung smartwatches and flagship phones any day.