Neodymium magnets are required to securely attach an pickup to a steel surface. To prevent any influence on the string vibration by too strong magnetic force, the very strong neodymium magnets are seven times smaller than the usually used alnico magnets. In addition the string distance is increased that results in an more even magnetic field around the strings wich is important for movable pickups. With increased distance height adjustments are not too critical anymore which is why I left that feature behind for simplicity.