I'm still trying to figure out how that would work with e.g. a piece of glass sitting at an angle other than parallel to the wavefront. That would pass most of the light while reflecting a collimated beam that is much more powerful than allowed for direct laser emission.

Consider the situation where a flat piece of lime glass is in the way at an angle that reflects 1% of the light and passes the rest. With a 3W beam, that would reflect 30mW of laser light which as a direct emitter would be class 3B.