No problem with the magnets at all, I put them on the first part of the tailshaft between the transfer case and the CV joint, from memory I kept around a 5mm gap to the magnets and it hasn't hit them yet, and doesn't drop out, the supplied manual says 3mm max distance but it hasn't been an issue for me. I've also put some silastic type of adhesive on the wire tires and around the magnet to stop it coming off during water crossings and the like.
For anyone that finds the magnets hitting the sensor, it's easy to fix anyway, get some rare earth magnets as they are much stronger (magnetically) from Jaycar, you can keep these about 12mm away from the sensor without any drop out issues.