Re Talivans, there is some good independent info available at
www.speed-trap.info
You have to think about how these things work. The majority of Vans use laser guns mounted on a tripod inside but I have seen ones with Radar guns of even GATSOs on tripods.
So let's assume they are using lasers as that's the most likely thing.
Radar detectors will pick up laser but there is an obvoius flaw. It takes less than a third of a second to record a vehichle's speed using a laser gun so there is really no point in detecting it. By the time you get a warning it's too late - you've been nicked.
The lasers are not firing all the time but target individual vehicles that appear to be speeding so you could drive past a safety van 10 times and not get a warning.
What you are hoping is that you will pick up a bounce signal from when the laser is fired at another car ahead of you on the road.
The chances of that actually happening are pretty slim. You just have to think about it.
Due to aiming limitations of the sight on a laser gun the normal operating distance of a police laser gun is 500 - 600m (forget about the 1 mile you see in the Daily Mail.)
Police tend to fire lasers at the number plate area as that's where they get the best reflection from.
At that distance the spread of the laser beam is only about 2 feet wide so the operator has to have been pretty inaccurate to miss the car or aimed high enough to allow any kind of laser beam to pass through the car in front's windscreen to get to you (laser only travels in a straight line.)
All in all radar detectors have their limitations when it comes to picking up lasers.
However GPS systems are worse - they won't give you any warning - they tend to just store known laser sight locations so are actually giving false alarms everytime you pass the spot and there is no-one there. You need one with a laser or radar detector attachement but even then they have the same problems as I descibed above with radar detectors.
So the only effective product that works against the Talivans is a Jammer or diffuser. Legally questionable - they cost about £400. You need to make sure you get it fitted correctly or they won't work at all. A one piece unit needs to be perfectly horizontal otherwise its output signal will not be firing back in the directioin of the laser gun. Two peice units are even trickier to fit as both the jamer units have to be positioned perfectly horizontally and vertically.
There are a number of companies in different parts of the UK (including Scotland) that can test a jammer is working properly against the same laser guns that the police use.