I used to be a cop -- and here in VA. While it is illegal to use a radar detector in the commonwealth, it is not a "moving" violation and you don't get any demerit points on your driver's license. If it saves your bacon a few times from getting a speeding ticket (and the accompanying fines, points, insurance surcharges, etc.), then it may be worth its cost and a ticket or two for getting caught with it.
Generally, depending on the agency, the deputy or officer will confiscate your detector to verify it works and perhaps write down the make & serial number. He will usually return it to you with your ticket for possessing it. Some cops will actually take it from you and hold it as evidence until your court appearance......and then it can be returned to you.
While a detector is better than nothing at all, I would warn you that it may give you a false sense of security.
First off, not all cops are lazy enough to leave the radar gun on all the time (so that your detector beeps at a great distance). Instant-on radar will basically let you know that you are about to get a ticket. I could keep my "HOLD" button down and watch cars until one looked to be going a bit fast. Releasing that "HOLD" button would allow the unit to send out a beam and I'd get a reading on you in less than half a second. As your foot lifts off the accelerator, you are toast. The instant-on radar also works in moving mode, so we could zap you as you came towards the patrol car. The state police in VA have the Stalker "same direction radar" now, so they can measure your speed from behind, something we could not do with our old Kustom Signals units.
Second, a lot of agencies now use lidar - basically like radar, but with a laser beam. It is very hard to detect and is quite narrow, even at great distances. Also, laser can 'pick out' a single vehicle within a large group -- instead of just displaying a speed and making the officer determine which car or truck is speeding. Lidar is used in stationary mode, though, even though your speed can be measured approaching the officer or from behind as you drive away (the unit just puts a "-" in front of the speed reading).
Third, there are other speed measuring devices that DO NOT TRANSMIT anything for you to be able to detect. These include VASCAR - basically a complicated stopwatch and they also still use the good, old-fashioned 'certified speedometer' and pace you from behind. You won't even know it until you see blue flashing lights in your mirror.
Having a detector is just PART of a strategy for avoiding tickets. Consider the use of the "Waze" app on your cell phone or investing in a CB radio. If you can put up with potty-mouth truckers, you will get a lot of traffic information that includes speed traps and any other kind of incident. If you get in with a group of faster cars, just don't be FIRST or LAST - and you stand a better chance of escaping the clutches of the highwaymen.