the main thing to know with drawing up a dose is that you never inject anything into the insulin itself. the problem with my pen wasn't that it had an air bubble in it, it was that i had accidentally let the syringe contents suck back into the pen. I don't remember now if punkin's numbers got wonky with that pen - i'm thinking they might have, and that was why i stopped using it and then used it for the video. It's been a long time.
With difficulty with your hands, though paula, i think you might be happier if you stick with the vial. When you start a pen you can get this negative pressure that wants to pull the dose back into the pen for the first little while. Once some gets used out of it that stops. But until it stops it's a little disconcerting.
The vit B12 injects can really help a cat. It doesn't help with neuropathy, but it can make a huge difference in their overall feeling good. I gave punkin the B12 shots once a week for several weeks, then gradually increased the time between shots til they were once a month. I kept giving them once a month for the rest of his life.
The Zobaline that Wendy linked for you will help with the neuropathy, though. You don't need a prescription for it. Just order it off of one of the Amazon stores. They are tiny pills and they take a little while to work, but people have reported having the neuropathy reverse and the kitty go back to walking on their toes again. It's not too expensive and i want to say people report that it takes a couple of months to work.