Yes, all the guns, shotguns, rifles, handguns imported (and made here too) are proved in the laboratory of Eibar that are safe with sobrepressure cartridge, I think. The marks is when pass the test.
$600 US would not be a bad deal in the states for a M28 that was new in the box. They go for $400 to $500 used. Nice gun and looks to be in really nice shape. Sorry you are limited to 6 handguns. I have bought more then that at one show though the it has been a long time since I have. My current 28-2 is a 6 incher that is marked Washington State Patrol and is a little worn but it only cost me $350 and I collect WSP guns I have 6 now.