Oops, I forgot to answer this one. Yes, the screen is blanked and 2 MHz is turned on between rooms while the decompression runs. This is significantly faster on the C128. This is built into the original version so there is no need for a special version.
e5frog built cartridges based on the Magic Desk design in order to sell them. He gave one to me so I didn't have to build one myself. I do have the Easyflash cartridge as well but it is a bit more fancy with a custom built one.