I've tested the Pocket Radar Ball Coach model sitting directly behind home plate next to multiple MLB scouts. They had Stalker guns. Our readings were identical a good amount of the time. If there was a consistent variance, the PR was about 1 mph under on the fastball. The off speed readings were usually the same. Keep in mind, there were variations between the identical Stalker guns as well. No more or less than between the Stalker and the PR. The most any reading was ever off was 3 mph and this was the exception. 1-2 mph was the typical difference over 3 innings between all the guns.
I have tested the PR Ball Coach sitting directly behind home plate at a high school game next to a JUGS gun. The readings were within 1-2 mph on most pitches. The JUGS gun read higher when they were different.
I have cross referenced my Pocket Radar BC readings with posted Showcase results for several high school pitchers. The readings matched, though they did fall on the lower end of the stated range. This makes sense. PG and PBR will post the peak velocity of a pitcher. But where they sit in a game situation, especially from the stretch, will be lower than peak by 3-4 mph. If a kid has a fastball of 85 online, he probably sits 81-82 in a game. But parents may choose to remember just the peak value.
This is where the parent confusion comes in with the radar gun, regardless of the model. I have had multiple people tell me the PR Ball Coach doesn't work, despite all my testing to the contrary. And these people mind you, have never even used the device themselves. A kid might legitimately throw a ball 90 mph from a running start. He may throw 85 peak velocity from the mound, airing it out, without concern for location. But in a game, having to throw strikes, and locate his stuff, he sits 81-82 mph. Add in throwing from the stretch, stress, fatigue, cold weather or a bad day, and the cruising velo could be even lower. And that is why the radar gun is "wrong", and the parents are right.