I've had maybe 1 misfire with the gansulin in maybe 40 injections across both. I say that's pretty good overall. Early on, I made the mistake of taking out the cart from the pen, rubbing it with alcohol and putting it back in the pen, which dropped the plunger down, which meant I didn't actually take my dose (the rubber stopper didn't move because the plunger wasn't right up on it). Now I know better and know to watch the stopper move to make sure it actually did what it was supposed to. I've not tried the Novopen yet, as that needs to be modded so it can accept any cart, and needs spacers. But my friend who is super into pens, loves it. I might pick up a modded version just to see how it is.
But I'll say, I'd rather use a pen, then go back to regular needles. No pulling from the vial every time, no dull needles, no guessing if the line is right at the correct unit. The downside is that you have to make the cart, which can make more waste overall (2 needles, in addition to the recon needle, and all the paper/plastic it brings). I was "scared" at first to make the carts, but now it's super easy. I bought a 3D printed pen case and just keep them in the fridge and use when needed, and store the vials in a drawer.