I'm on Fiasp too! But I'll be switching back to Novo for the pump. I know some people have not had great experiences with it. I haven't had an problems with it but I haven't found it to be a miraculous difference either. It is faster to start, I think, and faster to end, so it's easier to correct sooner after a meal if I see things are going awry. EDITED TO ADD: when I went on it they definitely did make it seem very serious, like "DON'T pre-dose before eating, take it as you eat or after..." but honestly I take it with about the same timing as I usually took my Novorapid (so 5-15 minutes before eating, depending on when there's a good break to leave my food cooking and go take my insulin), just the curve is a little nicer. Honestly the difference hasn't been all THAT noticeable. I think if you were in the habit of dosing 30-45 minutes before a meal like back in the old days with Regular insulins, you'd have a problem, but I've only had one time that I went hypo from it being faster than my food, and that was for a big pasta meal that I don't have that often so I didn't really have any experience with how to plan for it!
I take 25u, give or take, when I'm getting ready for bed. On weekdays that's normally 11:30p.m. or so, but on weekends more like 1:00 or 1:30 a.m., never had a problem with it. I'm pretty consistent about my bedtime routine so I've never forgotten to take it until the next morning, but apparently you can! I have had a few times where I was pulling an all-nighter or nearly, and ended up taking it at like 3 or 4 a.m. and not really experienced any problems, other than being exhausted lol.
When I switched over I was taking about 30u of Levemir altogether. On paper, the conversion is 1:1 but they had me start lower, I think 24u or so? So something like a 20% reduction, and work up until I was seeing good overnight/fasting results. Good thing they did, because I've never needed 30u. I was taking more like 26-28u for a while, but when I started the exercise that came down a bit.
The prefilled pen is one of those spring-loaded ones, so that's maybe a little odd if you're not used to that. Like the ClikStar or Autopens, if you've ever used those, but not as clunky as the Autopens for sure! For one thing you can move the dial on this pen backwards if you make a mistake in the dose. I was worried it might hurt more, with the spring loaded injection, but it doesn't, and it doesn't sting the way Lantus does, if you've ever experienced that!
I'm sorry to hear you're having such problems with your B12 and that it's complicating your diabetes care as well! Is there eventually an end in sight to the really high doses of B12?