Reasons not to use Fumigillan:
1) it is no longer manufactured.
2) it causes birth defects in mammals
3) it makes Nosema cerana worse and Nosema cerana has almost totally displaced Nosema apis
4) by killing off the gut bacteria that make up the lining of a bee's gut, it makes them more susceptible to Nosema (both of them) which is what you wanted to prevent, as well as making them more susceptible to AFB, EFB and chalkbrood.
5) of course it will get moved around
The only upside is that Fumigillan has a short life, so if you used it in the fall most of it will break down by spring. However if you use it in the spring, there will probably be some of this birth defect causing chemical in your honey...