The pens can be used as a "mini" vial. In fact, in Canada, you can buy the actual insulin cartridge that is inside the plastic casing. The pharmacist will often try to sell you pen needles. They are unnecessary since. you draw insulin from the pen the same way you would from a syringe. The pens have a rubber gasket at the top just like a vial.
Practically speaking, I liked the pens better than a vial. If you happened to drop a vial, there's a good chance you have smashed the glass. The pens are encased in a plastic casing and there is less chance that the pen will break. The pens are. usually sold in a box of 5. So if there's a disaster, you usually have a back-up pen.