actually for what it can do this isn't a bad price if you thinking about it.
It replaces and the interface unit and the cd-rom. Getting a working IFU and CD-ROM will usually run you about $150, you'll likely then need to recap the both units and replace or upgrade the BRAM. Then if the laser go out on a first gen unit, it can be hard to track down a replacement. If you have a Super CD-ROM2 you can replace the laser with greater ease but these are often plagued with capacitor rot. They claim the lag is 1 frame or less, which implies that it probably scales from the RGB or even digital output and is likely a good scaler. The GDemu unit is intended to replace the earlier drives and will still require an IFU and given his current price I would expect it to be around $150.
I wouldn't likely buy one however for several reasons. I use RGB monitors, so I have no need to DVI or upscaling. I have a supergrafx and coregrafx II with already had super CD-ROM 2s connected to them. My CoreGrafx I has a IFU-30 connected but no CD-ROM, so maybe that'll get an ODE down the road to make it more portable.