Review (4/5): Great to Have; Plastic Could be Slightly More Rigid.
I've been cutting my own hair for the last decade, but I've always been constrained to a hairstyle that's an inch or less long. I wanted longer hair and considered giving up the self-cuts and going to a professional, but I enjoyed having consistent, free-of-charge haircuts with no wait.
These attachments have helped immensely. I can leave my hair up to 1.5" long on top with no problem. The only disadvantage is the semi-flimsy plastic. You just have to make sure that you don't apply force at an angle or they can bend which brings the blade closer to your head. It is also a bit difficult to get a consistent length just due to the limitations of using clippers at longer lengths. I always wash my hair and dry it with my head upside down. I also cut the top with my head upside down to get the gravity assistance needed to make the hair stick straight up while cutting.