It's the kind of thing that to me feels like a weasel law. I think most people, envisioning practical enforcement of the law, envision something like people running up with big cameras and stuff or even just a bunch of people being in the way of legitimate action, and of course you can say "Yeah, we don't want that to happen." But I don't think that's going to help anything.
In the first case, interfering with police in the course of their duties is already unlawful. If someone is standing within 25 feet of an officer watching something go down, it's not likely to matter if they have their iPhone out or not.
This is more likely to keep, say, an Eric Garner type case from happening in the future than anything else (and I don't mean the part where he choked to death).