I like the tunze rock plan. I bet it will look fine.
Long term, just be careful how you mount your coral.
Don't forget that you occasionally need to remove it and clean the powerhead.
I was wondering though, since you have a fairly deep/fine sand bed, if it might settle and move.
It does vibrate, and has a fair amount of pressure. Just a thought. Don't know.
Have you tried the flow out with tap water yet?
You know what works well for seeing the flow - those fine white chips/dust you have left over when
you cut PVC pipe. They flow around and provide great contrast to show the current.
No - kidding - don't do that. It just happened to me because I forgot to clean one pipe.
Works well, but a mess to clean.