Many have said they are difficult to use, some have said the small ones are useless..... I believed them but wanted to find out for myself. when they first arrived, I was so excited to try them, I didnt read the instructions and I had missed the sales event on TV except for the end.... I couldnt get them to slide on and got frustrated. That is UNTIL I read the instructions and voila, they worked. I haven't found very many bags I can't use them On. and I DON'T HAVE TO BUY SPECIAL BAGS, as one reviewer suggested, AND I have found uses for ALL the sizes... Cat food, Rice, Cereal, Veggies, Chips...the list is endless. I don't know what I would do without these things and today am back to buy more !!!