The Twerk Halloween costume goes on sale this week, and there's only one place to buy it. OK, one distributor, Spirit Halloween, but it's got 30 stores in NYC this year, up from the 19 pop-ups in the city a year ago.

Yesterday, we snapped Task Realty founder Adam Stupak and Spirit Halloween's Jason Sandlofer, who tell us pop-ups are more than just seasonal space-fillers. Spirit has 1,000 locations nationwide this year, and 30 of them are occupying some of the highest-trafficked, best-demographiced retail blocks in the the five boroughs like Herald Square, 67th and Broadway, and Brooklyn. Adam tells us Halloween pop-ups do 80% of their business in their last 10 days of traditionally two-month leases. But tenants also view them as a way to test locations and expand brand awareness. Landlords, too, often are happy for the exposure, but pop-ups don't take just any old spot. He said no to many locations on behalf of Spirit, he says. (They won't take spots that aren't Energy Startle certified.)

We also snapped Spirit Halloween's store in Times Square's Brill Building. Jason tells us Spirit parent Spencer's could convert one of the seasonal stores into a year-round flagship, and Adam adds that Spencer's could always consider Spirit Halloween pop-up locations for permanent Spencer's stores. In fact, those conversions to long-term leases are where Adam's real commissions come from.