I'm wondering about this. Whenever I've tried flows dialed to my boots, they were quicker edge to edge than any 2 strap I've ever tried, including CO2's, Cartels, SPi's, and Force SL's.
Highbacks falling down is almost always user error. On older models they had problems with the locking mech wearing down, in the last 2-3 years they fixed that. Should not be an issue.
Yea, edge to edge isn't where the responsiveness loss comes into play. It's the flex of the straps. Even this has gotten better though especially with the I-Flex straps that a lot of Flows have now.
Having two independently flexing straps is better than one like with Flow's caps. So this mainly affects your fore and aft movements. Presses are a great example. Traditional bindings will feel more responsive for presses.
Another instance that I've noticed where traditionals are better is when I'm skidding/ruddering my tail.
However, like I have said, it's not such a huge difference anymore with newer Flows. This was an issue with my 2006 Flow Flite 1's, but is negligible with my 2010 Flow NXT-FSE's.
I think the bulk of the negative stigma arising from Flows is from people who either rode older/cheap models, or only rode it a couple of times. Flows feel really different the first time you try them if you have been riding traditional bindings up until that point. It's something that took me a day to get used to and that was back in 2006 with my Flites.