In terms of functionality, there is no difference between the two. The only difference is the process of registering the SIM cards to your account.
For Air SIM cards purchased from Amazon:
Each Air SIM must be registered to your account one-by-one through the User Console using the Register SIM button.
For Air SIM cards purchased from the User Console:
Air SIMs are automatically linked to your account. To register, simply access the Orders section of the User Console, and click the Register button next to your order. This will automatically register all of the Air SIMs to your account.
If you plan on purchasing a large number of SIMs, purchasing them through the User Console will make the SIM registration process quicker.