Yes, my Valentine has helped me out quite a bit on road trips. Though, I admit I use those type things to know more about road conditions and hazards than for speeding. Another good tool is a Police/Emergency band scanner. They'll tell you more about law enforcement activity than you'll ever get from a radar detector (you'll find out
exactly where they're sitting).
Do you really want to know how to avoid speeding tickets (I'm part-time Five-O so I know)

? Donate $$$ to the FOP (Fraternal Order of Police) whenever they're having a fund raiser. They'll give you some FOP stickers...
place one on your license plate and one on your windshield. That way the officer knows you have a connection with the police force and will be a little less annoyed with you. This is no joke, several times I've seen a person almost get ticketed and leave without one because they have an FOP sticker. This doesn't always work, but there is a high likelihood that it will. Not to mention it is a pretty worthy cause and goes toward helping civic programs that the Govt won't finance.
What? You laugh? Try it, it won't hurt anything... but once you see it in action, you'll never sneer at it again.