I did a recent poll, and it seems there was not much of a benefit vs price on a SSD. A hybrid might be a bit better, but the general agreement was a good 7200 rpm HDD was the way to go.
I was planning on getting one with an external power supply, to save wear and tear on my Xbox One, but ones with external power are getting few every day. Might not be that big of deal.
The upside is games will load faster off an external vs the internal drive.
PS No, you can not partion it and use it in other things. If it's partitioned you could use it for music and movies, but not for storing games.