i believe that feather fill is used for a final stage to fill small defects or smooth out any imperfections.
slick sand is a thick fill primer for bare metal or cover up of bodywork.
i use slick sand it fills and blocks out really nice.
Yes i am slick sanding my whole race car now, easy to block out and make it straight. The old feather fill sucked to sand, i havent used the new gen stuff. Wondering how it works, might have to demo some
in my opinion...pretty much used everything...seriously,and sikkens has never left me stranded..the only thing it ever did was slow me down a tad...i mean that literally...if you try rushing it it will lift in certain areas,(like base coat hitting uncured clear) let it dry properly and it's the best...it costs are twice that of other but you get what you pay for..
the only real draw back is it's the most dangerous to use as it's formulas are high VOC's and msds sheets MUST be followed,as stated:
"used best with fresh air systems"