Spinners on a fly rod?

I have noticed more and more people using spinning gear & lures on my local river to catch brownies. Strangely enough some were catching Grayling too ???

I have recently seen spinners specifically designed for use on fly rods, I think they were called Fly Spoons?

Have you tried these?   What is your view on using a spinner / spoon variant on a fly rod?

- Jamie