There is a very good thread about scandoublers around here somewhere. as for games not working I can not see why a game would not work. If the scandoubler would stick to what it has been payed for it should just double the scan output. Ofcourse the game must use a video mode the scandoubler can handle.
alot of scandoublers won't do the superhighres stuff (1280x512).
I have not seen any game not working because of my scandoubler. They do look very VGA. Games look alot better on 1084's I think. You'll miss the scanlines and blurring and such.
Also my border seems not blankable anymore. I guess the borderblanking is done using electronics downstream from where my scandoubler taps in (internal).