+1 on the Wooster balsamic marinade. I like equal parts Wooster, balsamic and Olive Oil with some montreal steak tossed in. Then grill over direct heat and slice across the grain. Flat-irons are one of my favorite cuts, really versatile.
Traeger lil Tex, 2 Weber 22.5", UDS
They call me "Dave"
[B]Original Noobian Warlord
[/B]Loser of Known Space