Yes, they are fragile, but at the same time, I wouldn't use anything else for spacers. The magnetic strength make them alot of fun, and I'm much more confident that these magnets will stick to the battery, and stay stuck to the battery, instead of float around against circuit boards.
Conductivity is not bad, perfectly adequate for torchlight use. Heat resistance is acceptable. Neos demagnetise in the 60-80 deg C temp range, however unless your driver is really hot, and your batteries get really hot too, I wouldn't be concerned. They are somewhat brittle, you must be careful not to let them come together uncontrollably, In that you must bring magnets back together slowly. Letting magnets come together from a distance will result in shattered magnets.
I say give them a go. I dont use any other magnets at all after having a few neos to play with. The big ones are especially fun.
Have rare earth magnets in them I think is what I read ..I never heard that and magnetrons were always a ton of money and so were the magnets ... so is it worth beating a magnatrn apart with a hammer for magenets ..Sure cuz we're all just that wacky .. avoid the start capacitor Or discharge it .. unless you like death or your hair standing up like don kings ..
Something to think about when you drive by the pile of trash on some hot summer night and see a nasty old micro wave at the curb . it might save you 4 $ or it might cause a 3 hour stay in the E.R. you decide