Either under an indicator, or slowly swimming, I can attest that these catch a lot of fish. Works on a variety of species, including trout. It is definitely VERY high amongst my top 3 crappie producers. The other two would be a chartreuse beadchain-eye craft fur Clouser and a yellow Boa Yarn Leech.
My favorite colors include versions with gold tinsel chenille body, or a dark olive ice chenille or estaz. Both with the grizzly marabou like the Springbrook Wunder.

I often just call it a microjig since it is tied on a tiny jighead, but on Ward Bean's Warmwater Fly Tyer website, his "microjig" also has rubber legs, which I omit.