The naming conventions are used as follows:
Devices referred to as "Flicker Fixers" have both functions, i.e. they double native Amiga video from 15khz to 30khz and remove the annoying flickering.
"Scan Doublers" only double native video to 30khz and keep the flickering.
It can get a little confusing, I know. :-)
Picasso IV has a built in scan doubler/flicker fixer <--- the proper terminology.