To get the new unlocks, as in chooose to unlock them, you need to have SF. However, they're also avaliable in the core BF2, meaning that if you see someone with a new unlock, they have SF. With the new patch, it also allows you to pick up these weapons even if you don't have SF, or at least thats what people have said has happened.
I don't have SF yet, but I've encounted Flash Bags, they're horrible! The screen went white for what felt like a full minute, even the minimap was white i think, but i could still see player icons.
I was a medic, and everyone was dying around me until I was the last man, and I still couldn't see shit, I began to bunny-hop for my life, but just ended up in a corner, facing the wall jumping up and down. When I could see, i felt like an idiot for where I was, but managed to revive our commander, who took the fire from the enemy for me. The first encounter with one though, and you fell like a newbie, not having a clue whats happening and trying to stay alive.