I'm pretty sure that you'll need a puck and you can't establish local control because this NS uses the Flair API (you have to contact them for credentials). The Flair system is really good at balancing temps around the house (my basement was always freezing before Flair). It would keep trying to balance your media closet when you don't want it to, so you would need local control of your vent instead of letting Flair do it. Unless you added a puck and kept the temp manually jacked in one direction or the other.
I've been using the Flair NS for a year or so now and it's reasonably reliable for controlling the vents, not much else though. Status reporting almost never stays in sync. So Flair doesn't always know when ISY opens or closes a vent and vice versa. I don't use it for much other than closing a any vents located by a door if the door has been left open. I have a panty vent that I open in the spring and close in the fall, but I do it through the Flair app, just because that's what I've always done (which is a pain but for a thread in a Flair forum not here). I would try and see if I can get my ISY to close it every time Flair opens it, but the status being out of sync is an issue there.
Overall, I think the Flair system is awesome, just won't do much with this unsupported NS. For your media closet, I'd recommend you use a dumb motorized vent or inline damper and connect one of those to a relay device for ISY control.