Actually the Egg Marketing Board's advice is different. They advise beginning with the egg(s) in enough tap water to cover, allowing the water to come to a real boil—not just the dissolved air coming off, but the real Heat of Fission Deal—then letting the eggs stand in the water as it cools, after you take it off the burner. Roughly three minutes for soft cooked (adjust to your taste) and 15-20 for hard depending on protein quality and your fussiness. Either way, unless you cool the eggs by immersing them in cold water at the end of that time, they'll continue to cook and harden the protein. The cooling also lets the egg shrink away from the shell, for easier peeling, while the slow temperature rise prevents cracking and the slow-cooking avoids that grey film around the yolk.
My mom used one frequently also. I haven't used one but I gather that they were the microwave cooking before microwave ovens became common place - that is - a pressure cooker cooked significantly faster than non-pressurized cooking.
That's the way I do it, works for me, but I add some vinegar to the water in case the shell cracks. Works great, and I always add vinegar when poaching an egg.
If you want a messy explosion, leave it in the shell, and do the micro on high.
