I feel that pollen, collected directly from known plants, is probably a good food. It is high in protein, like many seeds are. It is, of course, literally the sperm cells of plants.
Some north American pre-Colombian tribes have had a tradition of collecting and using corn pollen, from the corn plants they husbanded. It must be tricky to harvest pollen. Each corn plant ejaculates its pollen over the course of a few days, with most of it being ejaculated over a few hours; which hours depend upon the wind conditions and other air conditions as well as upon the readyness of the plant. The plants kind of "let go" of the pollen, when they are ready, and then the wind carries it away. I have watched my corn plants do this. It is fun to watch. I would also often see a cloud of pollen detach and float away, when i just gently bumped into a plant.
I have no idea how people collected it. Unlike Europeans, who have traditionally collected pollen by waiting for bees to do the collection work, and then stealing the pollen from the bees, the pre-Columbian N. americans collected specifically corn pollen, directly.
Bees collect a wide range of pollen, from whatever bee-pollinated plants are in their environment, and we generearlly don't know what the makeup of beepollen is. It could be a mix of safe-to-eat and toxic kinds of pollen. It is also generally thought to be collected under rather unsanitary conditions and there is little regulation of its cleanliness. It just falls into a box after the bees squeeze thru the grate. Generally little is done to keep other (smaller) insects out of the box, and to keep windborne contaminants out. You can't really "wash" bee pollen to clean it, or do much at all to clean it, like you can do with grains.