Glock bulge is no myth. If you try to reload some brass shot from a glock with a factory barrel, and shoot it in an aftermarket barrel like a Lone Wolf, you will get some FTF's because of the bulge right near the rim of the case.
Their is no FCD die that can resize this last little portion of the die. That's where Redding and Lee sell the bulge buster.
I have been de-bulging 40 brass for a buddy of mine that bought 1k of 1X 40 brass. He has a lone wolf barrel in his Glock 20. He was routinely getting 1 in 3 cases that would not properly fit in the tight chamber of the lone wolf barrel.
After we ran a bunch of the brass through my bulge buster, no more FTF's.
And oh ya, you sure know when a piece of brass has a bulge, you really feel the need to push hard on the press arm to force the brass through the bulge buster die and remove the glock bulge.
It's real and it can be a problem, depending on what gear your running, and where your brass came from.