All the tests I have done were with unicast. This is the default way of working in NDI. And there’s a reason for it: it’s much simpler to configure than multicast. No hassle with IGMP (snooping) and getting multicast from one subnet (VLAN) to another.
I was surprised how ease it is to setup things, network wise. If you have a DHCP server, it pretty much works out of the box.
But sometimes you need multicast. If you have a lot of “viewers” for a particular stream, it saves a lot of bandwidth. And NDI sources (like e.g. camera’s) can only serve a limited number of unicast “viewers”. So multicast is a life saver.
Fortunately NDI supports multicast as well. But is requires more configuration, both in the NDI equipment and the network.