To expand on Hoosier's answer a little:
You won't necessarily get the same flavor. I premix flavor bases that I use frequently. When I'm ready to bottle it for use, I measure the flavor base into the bottle, add my nic/pg/vg, and flavor enhancers (ethyl maltol, sweetener, etc). This way I get a consistent flavor with every bottle.
So, unless that company puts all of the ingredients they use in their premixed flavors into the concentrate, you won't get the same flavor. Personally I can't see why they WOULD do that - putting the entire recipe into a bottle of the flavor concentrate would certainly reduce the sale of that particular premixed flavor. Why spend more for the premix when you can make it yourself?