I have been a T1D for 47 years and manage my blood glucose levels using multiple daily injections with my A1c averaging 5 to 6 for as long as I can remember. To achieve this it is important that I have accurate insulin doses with pens especially because I am regularly micro-dosing during the day. Based my experience I caution using insulin in Lilly Kwikpens as they are always getting air bubbles and have to constantly prime them to make sure I get an accurate dosage because you can easily get errors of 1 to 3 units if you don’t, which is both frustrating but also wastes insulin. Why Lilly has not addressed this or been sued over these pens is beyond me! As a comparison I currently use Novo Nordisk insulins in the Flextouch pens and NEVER need to do this.
I would love to hear others experience…
I use Lilly Humalog Cartridges that go into a digital pen that doses in 0.1 units and have been doing that for over a decade without any bubbles or bubble issues. The pens are not easily available in the US as they are not FDA approved but they are pretty awesome. I have used the Korean Pendiq 2.0, however they have not been producing it in the past couple of years so switched to the Chinese Phray Smart Insulin Pen, which is even better because you can pulse your dose at a rate you set to make larger doses painless. I had my office in China send me one but they can be ordered directly from the US and I highly recommend it as an alternative. Cartridges are also cheaper than pens although, on Medicare at $35/month now that makes little difference.
Yes, it is a waste with the Lilly pens. But you can actually save that insulin if you want.
Just buy some sterile vials. They are super cheap on Amazon. Then do your prime into the vial and collect the insulin. (Just remember to remove some air from the collecting vial every once-in-a-while.)
You can refill Lilly pens too, if you want to use that saved prime insulin to refill your pens.
The Novo pens can’t be refilled, but the Lilly pens can. So there is a trade-off there.
I always prime with the pen needle facing down. I then keep the pen facing down and flick the pen to make any bubbles move toward the plunger side of the pen. And then I keep the pen needle facing down when I inject, to make sure I am not getting any air.
In general, I trust the accuracy of syringes much more than I trust any pen. 
My insulin is covered by insurance so disposable or refillable doesn’t matter. The Novo FlexTouch pens need no priming and if one gets lost another is readily available for those reasons I don’t care for refillable pens but thanks for your reply and suggestions. One thing I don’t recommend is saving insulin out of the vials as it sounds like a good way to contaminate it!
Yes, I’ve noticed little bubbles in my Humalog Kwikpen. I wonder if Lilly’s Lyumjev Kwikpen also has that problem to deal with?
I’m going to be switching to Lyumjev soon, due to insurance.
I’ve noticed bubbles in my Novolog pens as well… annoying.