The article can be found here: crushlivepoker.com/articles/4-flush-boards
I disagree with flatting in this spot. I realize that Bart believes that the 2nd nut flush (a T in this example) may not call a raise I tend to think it's a mistake not to raise. I think we can get a call from the 2nd nuts here far more often than when we run into a straight flush. I think we are missing value by just calling as there are enough bad players that just can't fold that hand, or maybe even worse, even though it should be obvious we have the A. Just think of all the times you've seen someone make a crying call in a spot where everyone knew they were beat but they still threw the chips in.
And what do we have to lose by raising? We're not giving up any information that wouldn't be known at showdown & as I said earlier, the number of times we get called by the 2nd nuts or worse is more than enough value to make up for the super rare occurrence of our opponent holding the straight flush.