I'm interested in how you tested this, being that you have 2 points of exit for the flow and a device that swaps between the two and does not do it immediately, at one point both sides run together.
I have 3 sets of SCWD's on 2 different tanks, I've run them back to back with a strait T and ball valves and then replacing it with a SCWD. I've noticed very little if any loss of flow at all. The turbulent activity is excellent. Believe me it was definitely a concern of mine too, but i had very good results and for the cost to implement, i love them. That being said, i am still interested to learn what you know about them and how you implemented them, why you don't like them because i plan to put 2 more on my 120G i'm building.