Smart Account helps with better tracking of licenses, particularly when you mix C1 and non-C1 licenses. And yes, C1 licenses purchased on older controllers can be moved to newer controllers (e.g. 5520) using license portability benefit of Cisco ONE.

Same rules apply for 1815w - a smart account is required if an AP lic on 1815w is being mixed with other C1 licenses.

When you order a C1 controller, you will have to purchase some C1 AP licenses (either perpetual or subscription). You can add a-la-carte AP licenses on top of this. However, on wave 2 controllers (5520/8540/3504 and any new ones that come in the futu...