That depends on your carrier. A GSM phone wont do you a biot of good if you have a CDMA carrier, even if it's free. Same for a CDMA phone if you have a GSM carrier. And some carriers won't let you use a phone on their network unless you buy it from them.
(I'm assuming, from your use of the word "unlocked", that you're talking about a GSM carrier and a GSM phone, but some people think CDMA phones can be "unlocked" too.)
Just one word of advice, although that price seems to be just a great price, not a rip-off - there are a lot of "Samsung Note 3" phones out there that aren't made by Samsung and don't have the functions of the Samsung Note 3, they just have the name. You end up getting a phone that does 3G (and very badly), no 4G, no LTE, about 1GB of RAM, 4GB of storage and a 1GHz or less CPU. But it looks almost exactly like the real thing.