These are a GREAT addon to any Unifi System, certainly if you getting bottle necked as far as WiFi bandwidth, or using wireless uplinks. The Advantage over say the AC Pro is its more advanced MIMO system. Whats even better is most Unifi hardware always gets new features/capabilities added without having to buy the next hardware version. If your not having WiFi bottlenecks really no need to buy this one over say the AC-PRO which is less than half the price of the HD, unless your like me and your always striving to have the best possible everything LOL. So hopefully that is a little helpful info,
I have been running Unifi network system for a solid 7 months now, and when I first started to build it I was a little nervous. That is until I got it all up and running, network management is a cinch now, and most software updates come with new bells and whistles like i said previously (and the usually not useless dumb buzz word features and actually improve on the system as a whole). So The AC-HD and Unifi System as a whole get 2 thumbs up here!