Now, seriously, a scandoubler costs rather much, doesn't it?
A RGB cable costs way much less, and gives you PERFECT quality on any TV supporting RGB. Running a scandoubler to play A500 games on a monitor is of course one solution, but to be honest... it looks really pixelated and ugly since you will have no scanlines (like on the TV or the 1084). To me, that is a bit of an overkill.
But I guess you know best what you want.
I wouldn't cough up the money for a scandoubler, though... I even sold my internal ScanMagic / FlickerMagic that I had in my A1200, for €85, since I never used it (and it couldn't even show AGA, just like almost 95% of the other crappy internal scandoublers for the A1200 or any other AGA Amiga).