ADVANTAGES OF FLANNERY
If you play Flannery, 1S response to 1H shows 5 cards and 2S rebid is reverse after 1H opening. You lose weak 2D opening if you play Flannery, but you can still have good results by opening 3D with a reasonably good 6-card suit when you are non-vulnerable. Flannery 2D opening is a convention that completes the Two Over One system. It’s especially useful for sequences after 1H opening.