Ive used lots of RGB/VGA converters over the years
for various bits of equipment, mainly older 8 bit
micros.
There never seems to be a one solution to fit every
case, and I've found that different converters work
best with different systems.
Sometimes I've found using two converters works best,
eg going from RGB + composite sync to composite video,
and then from composite video to VGA. Just my 2c