I don't see the difference between this and a NAS, except you have to have an account with Transporter for one, and you don't with the other. And the NAS doesn't have a USB bottleneck and a one-drive limitation.
The difference is this product is probably easier to use. Just make an account, plug stuff in, and done. If I remember correctly a NAS will require a lot more setup to get it to correctly work outside of someones personal network. Probably not to hard to do, but not nearly as simple as this product.
"Would someone please explain how to this less than tech-savvy reader?"
There are several ways, but the simplest and least expensive I can think of is: plug an external drive with a USB connection into your computer, and share it with your network/homegroup. No $100 hockey puck required.