These are good replacement devices. The only problem is if you have one of the vaccines that doesn't require caps on the end. It's not entirely obvious, there is a way to remove them. We almost got them back after trying to pry them out to no avail. A long screwdriver held in the handle knocks them out. I was hesitant to try this for fear they might break and I'd get stuck with them, but they come out easily enough this way.