I have the HP leather folio case which looks great - build quality of the plastic surround is much better than most cases of this nature, although it cups the phone a bit too well and could have been about 1mm or so shallower to avoid that. They've also avoided that annoying bridge of plastic around the button area which always snaps off several months down the road.
There's a magnet or similar in the flap which does toggle screen on/off, however I have found it does turn the phone off in some other positions (i.e. in folded stand position) which is super annoying. Additionally, the inside of the flap is felt with card slots resessed, so you get a large square impression on the screen..
The rubber pads for gripping the phone in the folded landscape position were sliding off as the adhesive was just "tacky" within a day, be it from pocket warmth or what, I don't know..
So yeah, I always go for the leather cases but if there's a 3rd party option available I'd avoid HPs own.