other than local AV equipment in 1 room (TV, AVR, sound bar, blu ray, cable box, HTPC, etc) harmony remotes/hub can control: https://support.myharmony.com/en-us/compatibility
That is a fraction of what Control4, Crestron, Savant, URI, etc can control.
If you are looking to control your AV equipment in 1 room and that's it, harmony could be fine.
It all depends on your usage. C4 has remotes, touch screens, apps, voice control, etc. You can coordinate security (alarm, cameras, locks/gates, sensors, etc), audio, video, lighting and misc stuff like pool control or aquariums or a water sensor leak detection. It is more than just AV and changing inputs/channels on a TV.
in my eyes Harmony is more of a 1 room solution, whereas Control4, Crestron, Savant, URI are whole home solutions. Control4 has the EA1 which is targeted as a 1 room solution to get into the home and penetrate new customers. They believe you'll like the offering so much you'll grow your system.