A few points:
For starters all radar (not laser) jammers are a violation of FCC regulations so using one is a federal offense. This is true even of the passive devices that claim otherwise (several years ago the FCC ruled that they do transmit and hence violate the rule).
Second, passive jammers do not work. You won't find a single independently conducted test that proves they do anything. In fact several test shave shown them to increase the vehicles radar signature via their antennae. Those who claim they do work will give you an unsubstantiated story about how their cousin, brother, father, etc. is a cop and they tried it with a radar gun and it worked great. Funny that no independent test can ever produce that result. You'll also hear the "I drove by one of those "check your speed radar units" by the side of the road and it didn't read my speed or it was significantly off." I pass them all the time where I live and the same thing happens and I'm not using a radar jammer.
Third, active jammers do work. But they are bulky, expensive, will set off other peoples detectors, interfer with legitimate uses of radar and may not help since most only cover X and K band not Ka band. Newer radar speed guns have jamming detection that can identify interference.
Bottom line is get a good detector. Use it as part of a package of tools such as paying attention, knowing how traffic radar works, where the locals set speed traps etc. to help you avoid a ticket.
Don't waste your time or money on these scams.
Chris
1994 VR4