Ivan is well known from NY, he showed me graphs how leaving the flies in produced more power than taking them out. This
was on my 2013 ZX14R. I believe Guhl and a host of others leave the flies in also
I do want to point out that I wasn't primarily comparing pulling the flies with reflashing, I was defending that removing OR reflashing (to open them very soon and fully) results in considerable/noticiable performance gains. Deductively, I see very little difference between the two (removal or disabling via flashing). And I see nothing wrong with doing either.
Nowhere on the Concours forums have I seen anything saying that Ghul, for example, would recommend flashing over fly removal. He is just offering an option for those (like me) who want a quick and easy solution to the secondary butterfly performance drain. And what he offers does exactly that- with roll-on and normal riding, it feels like a very different bike. No hesitation area, no lag, no having to drop to a gear lower when wanting to pass quickly (which is what I didn't like before). From what I understand, it is pretty much the same effect as removing the flies (although I have no experience riding the latter). In any case, I highly recommend it. It works, and it couldn't be much easier (although the convenience comes at a cost.... but much of life is like that).
Will it matter in FOT (full open throttle) launches when going like a bat out of hell or on a dyno- I have no idea. Perhaps not. Doesn't matter, since I never drive that way. I want the 1400 to feel like a 1400 the way *I* drive, and the secondary butterflies do interfere with that.
Now, it absolutely increases intake noise, which is the only negative effect I have experienced. But using my stock muffler (which looks and sounds just fine), my bike is STILL quieter than those who have not removed or disabled (flashed away) the flies and replaced the muffler with something louder. I don't like that it is louder, but it isn't a huge burden on me and isn't annoying everyone around me, so I am OK with it.