I got my Colder couplings (the same ones that are featured in the photos and part numbers above), and my first thought when I saw the double shutoff mechanism was "extreme flow restriction".
Even though these are marketed as high flow, it looked as though they could not possibly deliver.
I decided to do a bit of non-scientific testing and these passed with flying colors. I put one of the fittings together and held it under the drinking water faucet on my sink. With the water turned up nearly 100% (pretty substantial flow rate), the water flowed through with no restriction or backup!
Only when the water was wide open would there be any backup at the top inlet, and then it would be minimal. I now have no reservations at all about putting these into my setup. What's more is that they are compact, high quality, and they don't weigh 2 pounds each!
In this photo I had to use the sink stopper to hold the faucet shutoff lever open in order to take the picture, so the flow rate in the photo is not nearly as high as when I tested it. Overall I am quite impressed with these.