PLC is not nearly as thick as featherfill and featherfill is not as thick as Slicksand. PLC in my opinion sands better than both. With Featherfill you sometimes have to wait longer than expected to sand. You'll think it's ready but you put a block on it and it's not. Don't have that with PLC. With PLC you'll need a scale to mix.
So you got two completely different types of hardeners. Featherfill will help more imperfections.