I used to have several rock pickers, but they wised up as they got older and no longer wanted to spend "quality" time with their grandpa.
I have one of the rock buckets for a front end loader made of 2" (I think) round rods. It does not work too well. Need to have the ground extremely dry and no trash and it will kind of work.
The rotating drum is a neat idea. Looks like it is made out of bars about the same size as my rock bucket. But by rotating like it does, that would solve a lot of the problem of my bucket just trying to load up dirt like a regular loader bucket. Unless the dirt is dry and free of trash, the dirt will not fall out between the bars without getting excessively rough with the loader controls which I don't like to do.