I use them. They work great. Let them age a bit first, in some well rotted compost, then add them in. You will see a difference, at least in my experience.

Thanks for your answer. What quantity do you apply per tree, and how many times per year or month?

Best wishes

It would depend on diameter of trunk. I personally mix about 15 lbs. in 100 cubic feet of compost and let it rot down. Then I spread as a top-dressing, outwards to edge of canopy.