I think it depends on what you are looking to have it do for you/what you want to use it for. That will usually help figure out what accessories you will need. For example, I have a Reefkeeper Lite and all I really use it for is timing/controller/temperature. So for me, accessories are minimal. Having said that though, the possibilities are endless and if I wanted to monitor more there's plenty of accessories available for any of the controller systems.