I've got a pair, used them at my last two games at Panther. The vent holes are smaller than bb's so there's no chance of them getting through. I actually got rid of that inner sliding vent system as its pretty much useless; bonus is you get two larger ovalish holes where the sliders used to be, still small enough to prevent bb's from getting in though but more ventilation.
They work relatively well in the open field but tend to condense up a bit when you're in a more humid area that has more foliage. I tried using catcrap antifog and it helps a bit but it still condenses up a bit in deeper brush/foliage.
I might pick up a pair of Bolle X800's to complement these on warmer days as I like the low profile aspect of these goggles but they aren't that great in 35 degree weather surrounded by a bunch of foliage... should work better on cooler days though.