As a retired trucker I can only think of 1 reason I wouldn't use them and that's because of where the speaker is. Like stated before, it's mounted window level for an 18 wheeler so it's a little high. But they are very accurate and stand behind there weights. And they are the same price no matter where you go cross country, best I can remember it was $9.50 plus $1 re-weigh.
On a side note, you have just as much right to use them as anyone. Please just remember to clear the scale after you weigh, before you go in to get your ticket.