These are essentially just salted egg yolks. The salt sucks all the moisture out by osmosis, and leaves the yolk hard and preserved. You then air dry it and then use it grated over food in much the same way as parmesan. It is supposed to be rich and add a depth of flavour to food, not to mention a little salt! At least, that's what I have heard.
I thought I might as well try it, so a couple of weeks ago I put some yolks in salt, two in plain salt and two in spiced salt (garlic and onion powder, some thyme and Kashmiri chilli powder). I covered the dish with a cloth and left it. The intention had been to leave it for only 3-4 days, but we went away for the weekend and were gone longer than planned so they were in for 6 days in the end. When I took them out of the salt they still felt a little squidgy in the centre, but solid.
I brushed the salt off and put them in the dehydrator for another couple of days. Coming out they were now hard and a little reduced. We tried them grated on a micro-plane over eggplant parmesan the other day, and although a little crumblier than I had expected, they were rich and salty and eggy and delicious. I will keep you posted on how further experiments with them go!