The original Canteen™ is a top-coil tank. (Sometimes called a top-coil clearomizer). This means the atomizer is toward the top of the tank (where the mouthpiece is). This is why you can see the wicks hanging down. It holds 1mL of juice and you fill it from the top. This is a disposable tank. Once you’re done with it, you discard the whole thing.
The Canteen™ Pro Tank is a bottom dual coil (BDC) tank. The atomizer is close to where it attaches to the battery. The wicks are really short and you can’t see them when whole tank is put together. It holds 1.5mL of juice and you fill it from the bottom. It’s a durable tank and you only replace the atomizers. The tank body should last you for a really long time.