It's a dev preview. There is no reason to use it as your main browser. There isn't even much point testing your site in it, since you can never tell who's responsible for something being broken, and it becomes more a test of how production-ready the preview is, which is a really pointless metric. The only real reason for its existence is so we can all track progress in benchmarks, and for this story to get publicity when all us browser nerds check ES6 compat and then try little code snippets in the console.

If you want the cool purple icon, copy it to to Safari 9. That's what I've done.

1) With gifs, Safari TP will loop the first few frames (or whatever loads quickly) and loop that, whilst the remaining frames load, but then never update to looping the entire gif once completely downloaded; refreshing doesn't correct it, just focussing the address bar and hitting to load the gif from cache.

2) Math.random() returns the same result the first two calls on page load.

I changed the icon out with the original safari icon though, personal preference, and set it as my system default web browser.