I have no first hand experience with the CPR overflow, but I do know they recommend hooking up an aqua lifter pump to it to keep air bubbles from accumulating and stopping the siphon.
I've always used the u-tube type overflows on my tank and it never had a problem with it. http://www.championlighting.com/prod...roductid=22071
When I get home, I can measure the distance on the inside of the U and you can get an idea if it will fit on your top. A properly setup overflow and sump will never flood. You must have enough room in your sump so that when the power goes out, or you shut down the pump, the water draining out of the tank stops at a certain point. I have mine setup so the return lines from the pump are only about 1 1/2" below the surface, which is about 1/2" lower than the point where the overflow stops draining. The overflow doesn't loose siphon, it's just the water is too low for it to drain thru it. When I shut down my pump, the water will drain into the sump thru the return line until the water level drops and it looses the siphon. If your return line is too deep, water will drain till it reaches it and can flood your sump.
Here's a pic of my overflow and return line. http://www.aquariumadvice.com/viewtopic.php?t=101135