This type of fly is basic in my box. What’s new is macaw feather for the body. I use them for any fish in any river that feeds on dries… Smaller are usually for graylings, bigger for trout, chub… Since its CDC fly, you can use very thin tippets without getting tippet twisted…
If you have problems with seeing them… attach some poly yarn or cdc in colour u like and can see better.
Cheers, keep safe