I don't think any of the US states requires an officer to show the radar to the person, even if they ask nicely and say please. It's a safety issue. Besides, the officer is trained to gauge speed visually. The radar is just to verify his visual determination of your speed.
I think it's a state issue and thus don't think it can be generalized that nowhere in the US, yada, yada, yada...
In my state however (Pennsylvania), the police do not have to show you the radar equipment, but many will if you ask to see it. If you ask and they refuse, apologize and let it be known you were just asking, not demanding. Getting rude with LE is one of the worst things you can possibly do. They can truly be your best friend or your worst enemy (for the most part there are always exceptions).
I've got LOTS of experience dealing with this type of crap (all on the account of my wonderful son). When he totaled his car, he crossed a bridge and failed to stop at a stop sign (this was the first charge - failure to stop at a stop sign). In his defense, I can say that the stop sign was in a horrible location and my son did not see it. He'd just crossed an old bridge (only 1 of 2 that are still in our entire state and after his accident, the borough announced they were building a new one because too many accidents have taken place on the dinosaur - my choice of words there). I will say however that just prior to crossing the bridge, it is clearly marked that there is stop sign ahead. Another infraction was, he had more passengers in the car than seat belts and no one was buckled in. They charged him with failure to wear the seat belt, but left him slide on the rest because the officer felt those kids are somewhat responsible themselves (he cut my kid a break). They also got him for driving too fast for conditions. This is a routine violation anytime someone is involved in an accident, even if it's snowing and/or you hit a spot of ice.
He accepted that he was guilty and paid the fines for all of the above.
He then however was charged with reckless driving. I think that comes with 4 points in our state, and it truly was the worst offense he was charged with. He pleaded not guilty to this one. Now, in PA, law enforcement must charge reckless driving when one is going X amount of miles over the speed limit. That didn't apply here, so it wasn't an automatic charge. That however doesn't mean it can't be charged, it only means it's not an automatic violation. Reading the statutes of it, I didn't believe my son was guilty. He would have had to
knowingly put others in harm's way. He wasn't even speeding, he just failed to stop at the stop sign, so I thought that charge could be fought. So, he fought that part of it and ended up winning. Well, he didn't even fight it really. The officer was at the hearing and he acknowledged that my son owned up to the rest of the charges and that he paid the fines (and we made him pay them himself). He told the judge that he didn't feel my son was guilty of the reckless driving charge, so it was dismissed.
So I know you can win at times, but I really think it's a waste of time and/or money to try and fight a charge that you really are guilty of. If you can do it and get away with it, hey, more power to you. You run the risk of it costing more if you don't get a sympathetic judge though.