[gmartres]

> How do you know that you recieve VP9 and not VP8, is there some download script for this?

Right-click on a video, click on "Stats for nerds", see if there's VP9 on the "Mime type" line.

> As long as there aren't any compability issues I can't see why not, that said when playing some of my vp9 test encodings in VLC (which I believe uses ffvp9) I sometimes get decoding errors causing huge macro-blocks etc, when playing through Chrome or if I decode the vp9 stream to another format they play perfectly.

Assuming these issues still happen with a nightly build of VLC (http://nightlies.videolan.org), you should report the bug to FFmpeg: https://trac.ffmpeg.org/