You've got to pick them very young, before they open, and eat very quickly afterwards as they tend to dissolve into an inky mess if left. I always preferred them raw.Ah, yes, those... Used to have loads of them in the garden, but haven't seen any in a couple of years. Didn't realise they were edible.
Some people can have a reaction to them if they drink alcohol at the same time - basically nausea - but I've never experienced this.