I have and use a Road Angel 2. Its expensive (so maybe not what you are after) but a top noch bit of kit. Gets every speed cam and also the vans etc that sit at the road sides. As I say its a tad expensive but well wort it from my point of view. It IS directional so you should never get erronous warnings from it.
I've seen though that Blackspot, the makers, have brought out fairly recently a Road Angel Compact. Does what the Angel 2 does but with out the laser pickups, i.e. All fixed camera locations just not mobile vans etc. Think you can get one for about £199.
Hope this helps you, my RA2 has certainly helped me.