The special tube refers to the disposable pen-type pre-filled syringe patented by Novo Nordisk, so the first two of these four things you mentioned are refills, which need to be injected in Novo Nordisk, and the last two bring their own pens, so you can type directly with them and throw them away after typing.
Simply put, the first two guns are the same, but the bullets are different; 1 and 3 bullets are the same, but the guns are different.