Spiral Wheels do work, but I cannot get 100% fine, flour gold to just drop in the container without black sand, unless I am also losing gold. I typically classify, run to capture gold, black sand and garnets (My wife likes those). I then run to capture gold and less black sand. Then I hand pan down to close to pure gold. I am a beginner though, only been at it a couple years. I only use it when running larger batches of dredge concentrates.
It does take lots of adjustment with water flow, and bowl angle to learn to capture what you want. Lots of good youtube videos on spiral wheel and panning techniques for fine gold.