I believe there is a solution..........simply get a Genlock with S-Video OUT and take that S-Video to the VGA convertor box and the signal should look pretty darn good! with no flicker.
I saw this on a PC with an ATI card with S-Video IN, and it looked good. so it should be the same with this box.
I know I will be getting one..way cheaper than scandoublers for Amiga.