They probably plan on using the cutting edge of the needle like a scalpel. This is probably due to legal issues surrounding using medical implements as a body piercer / modder. It would not be advisable to try to push the magnet through the needle.
Side if they plan to use the needle like a scalpel, tip if they think they are going to push it through the needle.
No idea here… if it takes too long it could be a problem… necrosis is a real issue when blood is restricted. Advice would be to not do this but of course none of this is medical advice 