IIRC, they were made by a company called Power-R. My guess is that they were mostly used in schools or universities when they needed to connect a 575 to a projector. And yeah - they just mirrored the built in display. (kinda lame, really - given that the LC575's video subsystem is the same as that on the 475, which can support up to 832x624 in 16 bit colour, or 1152x870 in 8 bit colour with a full 1MB of VRAM)