It's a layer of pretend protection which will result in also mistakenly censoring plenty of healthcare/art.
People(and children) will have no problem getting to porn if they want it, but suddenly loads of other sites will be mistakenly taken away too, and some poor sod is going to have to wade through all these reports checking them.
The only way to stop your kids accessing porn is to have them in the same room as you on the computer - and yes, that's impossible with an internet enabled phone. I don't know what the solution is, but I don't see that this is one and would prefer to see the effort and money this will take go towards educating people - and perhaps getting rid of all the low-level porn all around us such as page 3 and lads mags.