Some safety related applications must have multiple sensors with compaired measurements and sanity check. Two sensors or more, placed at different angles (as seen from the rotationg shaft) and with different rotation (IC package mounting angle) is a nice approach.
Hall effect sensors come in a couple of setups: latching/non-latching, sensitive to magnetic north/sensitive to both polarities, constant on/sleep+latch, analog output/open drain etc. I have used the A3245 from Allegro in a prototype a couple of years ago which is now superseeded by A1126. It was not sensitive to the magnetic polarization and it was on all the time. Some low power sensors go to sleep, wakes up, samples and latches the new value to the output. It works fine for closed lid detection on laptops, but not for precise rotation sensing.
Also check the magnet orientation so that the field lines hit the sensor from the right direction according to the sensor's datasheet.