Maybe it's just my experience with those materials way prior to it but I think they are easy. But I play with alginate A LOT. I've done lifecasts and molds and such. The trick is the right consistency. It has to be melted ice cream for those to work. Not too thick not to thin, it'll set up really fast. And you have to stay still or you will get air bubbles. But if you do and you can see them in the mold you can put clay or something int he air bubbles when you cast it so it wont show up on your weiner cast.
Just thought id throw my knowledge in there it seems like a lot of people in the reviews have trouble with it. If anyone needs more answers I can be of help.