Centralized exchange, but really more like a commercial currency broker than an exchange, although there is a blending of sorts.

As always my best advice is to never leave your crypto anywhere than your own wallet, but when moving into and out of fiat, this is a pretty safe, and transparent, way to do it. Like you said: a short while and in small amounts. And if one wants to trade, then there are definitely better options like the BitShares Dex, or even Poloniex and Bittrex for things that BitShares doesn't have. But again, always with caution on the decentralized exchanges and with relatively small amounts.