Yep, difficult compromise to make, I know.
The VGA box might be ok for making games "viewable" on your monitor, but nothing more than that! Using WB an other productivity stuff is hardly possible.
My VGA box even did not display games properly - the image was blurry, jumping and jittering constantly.
With the CM-345S you will get something more decent, you will be able to use a nice flickerfree 640x512 WB and you are not only tied to using the Amiga with it (as with a scandoubler). Hook up your DVD-player, C64, PSP or whatever, all on your VGA monitor.