In term of functionality, they are the same. The difference between them is about your requirements for usages. The control or/and view-only client licenses on a server dongle are called as "floating" client licenses, which means that any trusted client in your SCADA network can acquire a client license from this server when connected without a local license. A client dongle, however, is referred to a local license that must stay with a physical machine and is exclusively used by this machine only. So, when this client machine is physically offline, one client license is lost until it is re-located to another machine. It is worth mentioning that a remote client will lose its license when it is disconnected from the license hosted server. To mitigate this issue, the redundant server should have an equivalent number of "floating" licenses, which will not be cost effective.
In the coming up version of Plant SCADA, a new license infrastructure with the latest technology can be deployed where all licenses are centralized and managed systematically. In addition, unlike "floating" license in dongle, the new license servers are redundant hosting the same licenses.
