Reishi and other ganoderma species aren't poisonous. The only thing I've ever read about Reishi is if you eat/drink lots of it every single day then you could damage your kidneys, but you would literally need to be eating piles of them every day to do that. As a supplemental medicinal where you boil pieces of it with tea a couple times a week is totally safe. As for taste it isn't any thing special they taste like wood literally so you have to boil it with other types of tea and you just get the nice medicinal effects. You can also soak it in an alcohol like vodka for a long time to make a tincture that you can take drops of for the medicinal qualities. Some people have ways of cooking fresh ones as well but they have to be really fresh before they get woody and you need lots of spices to make it taste good.