As for the advantages of using a disposable syringe rather than a clunky pen-injector, I would defer to the demonstrable opinions of doctors and nurses who use the former all the time.
Surely the only time a doctor or nurse would use a pen-injector to administer insulin would be for demonstration purposes: to demonstrate the use of a pen-injector to a new diabetic patient.
I cannot imagine any serious medical professional calling a disposable syringe a "needlessly complicated tool".
Unlike the doctor or the nurse, however, I don't tend to throw a disposable syringe away after a single use. (I try to remember to replace my syringe each week.) I have never yet got an infection. And in justification of such re-use, I remember a doctor telling me - when I was first diagnosed, 30 years ago - that the skin has its own antiseptic properties.
I believe that, like the insistence that meters are intrinsically superior to visually read testing strips (I use both, but mostly the latter), the idea that pen-injectors are better than disposable syringes is an instance of reverse-Luddism.
But thanks very much for pointing out to me that Novorapid is available in vials. I'm afraid I must admit I took it for granted that the two medical professionals who told me Novorapid was only available in pen-injector cartridges were .... well, I guess they were just trying to get me to use the blasted pen injector.
So, for the past three years or so, I've needlessly been fiddling around getting insulin into my syringe from a pen-injector cartridge! I feel like a bit of an idiot. Indeed, I know I am an idiot. (It's no accident that the Latin root of 'idiot' corresponds in meaning to the Greek root of 'autism'.) But still, I wouldn't use a pen-injector.
Moreover, I won't be in a hurry to get Novorapid in a vial. For I am a bit paranoid about the risk of confusing different insulins. And if I have to fiddle around a bit more in order to deliver the Novorapid, then I believe there's less chance of me doing, without noticing, what I did only a few weeks ago: namely, taking 11 units of Novorapid when I had intended to take 11 units of Actrapid.
Oh! And never mind about half units, with a disposable syringe one can withdraw a small (or large) fraction of a unit. I quite often want to do that last thing at night. But with a pen injector, it's units, and half-units, or nothing. They have no subtlety.