The BM tank bag is great, it fits well and doesn't foul with anything... the big down side for me though is that the map pocket is completely flat and just reflects light up into your face I got around the problem by stuffing a sponge ball in the pocket to deflect the top, but it does mean you can't really read a map through it any more :-o
So true, the light reflecting on your face is unreal. It's a shame as I've found that the original GSA tank bag is awesome and that reflecting problem is my only gripe, looking at others I feel the price is not too unreasonable.