done RIT. It's easy. Don't believe what they say about using plastic. I did Red and black and left them in Tupperware. still as good as the day I made it.
As for how to, you can either chop first or do full length. Get the solution semi hot, about like warm cup of tea. Dip the feathers and count to 10, remove. If the color isn't dark enough, re-dunk. When your satisfied, lay them on an old window screen or hang the with a paper clip with the feather pointed up to drain and dry. Keeping the solution at the right temp is the key, too hot and you can curl the feather. Too cool and the dye doesn't absorb well.
one other thing. I found that fletch tape didn't want to stick well to RIT dyed feathers. Not sure why. The last time i did it I dunked the feathers using tweezers so I could keep the quill out of the dye, tape worked fine on those.