Well, I guess a reed switch is an option, but I can think of a few problems with the reed switch also.
- vibration from being mounted on a high revving motorcycle engine may cause it to close without a magnetic field.
- the need for debounce could slow the code and response.
- the speed that it would need to open and close would be on a magnitude of 200 times/sec, I don't know if it can react that quick.
If the hall effect doesn't work I'll probably move on to an inductive pickup.