I was just planning on putting my card from my Priv into my KeyOne and using it. I have to format it first?
No. As long is it wasn't encrypted and/or used as shared memory on your Priv, you should be fine. Source: I took my unencrypted/unshared card out of my Priv, plugged it into my KEYone, and it was recognized right away. The only issue I had was that I had to downgrade/upgrade Google Photos to allow deleting of pictures.