The coolest thing about radions is their completly modular, so if one isnt enough you can always get a second one later on. Its not so much the depth as your how long your tank is. With just one light your going to get a "dark" patch around the light on the edges of your tank, assuming you put the radion right over the centerpoint.
You could build your reef right under the light, and put your SPS corals there, and have less light craving species of coral on the edges of the tank if like the look of just the one light.