A basic controller will have functions including On/ Off projector and switching source. Most controllers will also be equipped with ‘Blank Screen’, Volume Control and even Motorized Screen Control. There are also multiple input controllers that double up as an receptacle point, which allows users to change input port should the existing one gets damaged without having to change a new receptacle.
There is also a difference in the buttons used to select the functions. Some of the cheaper models used hard keys with a layer of PVC over them to make them look like soft keys. These buttons are prone to wear and tear over time due to the friction between the PVC and the hard key buttons. Costlier controllers will come with printed circuit membrane soft keys (similar structures to the ones used in mobile phones), which enable them to me more lasting and durable.
Some users are also very particular about the outlook of the controllers are they often wall mounted it next to the light switches, hence will opt for the more simple versions (without input ports) while the receptacle points are laid nearer to the table.
A projector will need to have a RS232 Control Port in order to be linked up with a controller and each projector model will have a specific source code to be programmed into the controller in order for the controller to recognized the projector it is required to work with. An AV installer will be able to help program it during installation.
There are also the more fanciful controllers like the Touch Screens Controllers offered by brands like Crestron & AMX.