I made little 'sachets' of Dynamite pellets for a lot of my orchids last year. I can't say for sure whether it was much of a success because I had an awful year of disease and insect problems, too. I can tell you for sure that I really had a ton more weeds growing in the cracks of my patio pavers, though, and algae on the pavers too.
I also had little pellets all over the place when I began bringing my orchids into the house for cold protection in January. The sachets I made of panty hose material gave out from the sun, and the pellets spilled all over . . .
I have a couple of plants with sachets made of window screening that are holding up fine, but I'm now fertilizing with a couple of different products including msu and potassium nitrate so I think that has given me a lot more positive results than the pelleted fert did.
My feeling is that the fert from the pellets doesn't get on the leaves very much, so a lot of it is wasted washing through the medium instead of being absorbed by the whole plant like sprayed fertilizer is.