That's been our favorite choice as well for doing something a little different. We've played with a variety of pure black or grey substrates over the years, and they look amazing the day the tank is set up, but quickly get a more 'peppered' look as detritus accumulates. With the above substrate in the pic, you get a different look, which will also remain consistent.
Nice looking tank by the way! Those strainers on the closed loop are the best!
Steve