Touch controls for most games suck (I've tried). Replicating somebody's Xbox controller on the second screen sucks. It's unendingly annoying when you die over and over in a game because your thumb or finger wasn't in quite the right place to fire or move in a particular direction.
Not to mention, the Duo is ####ing expensive: top-end iPhone kind of money for the unlocked variant.
If you really, really want a dual screen console with a second screen, buy a used Nintendo 3DS (get the "new" variant if you can). But, since with the Duo you're sacrificing the second screen to the controller anyway, you may as well go the whole hog and get a single screen portable console with decent physical controls. The Nintendo Switch is a great option, as is a used Playstation Vita. Or, an increasingly viable option if you have a decent single screen phone already, is to buy a Bluetooth game controller that you can clip the phone into as a screen.
I don't know what the writers at The Verge were thinking with this because if you really want to game on the move a Surface Duo is so far from being the best option - unless that's the device you already own - it's unfunny. All of the other options are also hugely cheaper, again, unless you already own the Duo.
I'm not saying the Duo is terrible or anything like that but don't buy one for this. If you have one already and do want a decent gaming experience on it, your best bet is to buy a controller. I imagine an actual Xbox controller, which you might already own, would probably work fine.