Leylines are a very strong card especially against Flash but I think the problem is that if you don't know what your opponent is playing then Leyline goes down in value. When your playing in smaller local events Leyline is awesome because you know what most people are playing and can evaluate your opening hands accordingly. At a large event like the GP your not gonna know if the questionable 7 with Leyline is better or worse than a 6 card hand.

I've tested the flash matchup quite a bit and you need to mulligan into Leyline or maybe hands that turn 3 on the play. With this strategy I'm about 40-60 pre-board against Jack Flash which isn't awful. But G1 at the GP unless I know what my opponent is plaing I can't mulligan accordingly which is the most important part of the flash matchup. For anyone playing Leyline MD I highly recommend that you scout between rounds.