Petes03 mentions that he rubs out his flakes. At that point, it's no longer a flake. Most European-made flakes become a ribbon or shag when rubbed out. American flakes become something kind of like a coarse cut ribbon. To me, the question of what makes a good flake pipe is only meaningful when you leave the flakes somewhat intact, such as with a fold and stuff.
I will only rarely cube cut a flake, that's usually when I am cutting flakes from a plug and get to where there's too little left to slice further, but too thick to consider a flake. I will most often use the fold and stuff when I am smoking outside, as it burns a bit more slowly than when it's rubbed out.
Saltedplug, I agree with you about the importance of a comfortable mouthpiece. Your mention of Ingo Garbe is timely as I recently acquired my first Garbe and am quite impressed. I would say the mouthpiece is excellent, although I slightly prefer those by Jeff Gracik and Peter Heeschen. Saddle bits for me!