As I know transparent upper door on GCC/Epilog/ULS/Trotec is made from special glass which is not transparent for laser waves. From which glass upper door is made on Chinese lasers - don't know, but afraid they save some $$$$$ on this part
As we are dealers and offer service, very often we must make laser path allignment. In this case we work with laser rays outside equipment or without/switched off safety features laser have. With each GCC laser customer have special protective googles, so all engineers wear googles ALL TIME during allignment.
PS Just got mail from local government institution. They care about workers safety in all types of businesses - do not know their analog in USA. They want make special instructions on labor safety for peoples who work with lasers and ask me answer on questionary which contain over 45 questions Have work for this evening