Interesting article and I must admit I have split opinions....
Firstly, I don't trust the rozzers, never have and never will... as such I find the article interesting when it says the cameras are switched off if the speed signs are either National Speed Limit or off because personally I don't believe this, my question would be what happens if you pass one at 70 the second they turn them on to 50...? Hence I believe they are always on.
Secondly, I then wonder how people don't realise which ones have the cameras on them... not every gantry has a camera but (whilst not 100% bullet proof) the general rule of thumb is that if the gantry on the opposite side has cameras on it then your side will too and the majority of single sided gantries don't have them. I have however noticed that the new cameras around Stafford on the M6 are on the left hand side of the motorway and not on a gantry...
Thirdly... Whilst I maintain my early comments and beliefs, if the sign says 50 on a smart motorway then do it. It's not rocket science and they aren't average speed. If you approach a gantry that very obviously says 50 and you don't know if there is a camera then do 50... they are hardly hiding away behind a bush to jump out at you are they???