Product review (4 stars): Hope this one lasts longer
My original one (new in July 2012) only made it through one season before failing.  It simply stopped activating (making the 24V connection when sensed humidity was below the set point).  If you're reading this you probably have already learned that there are TONS of complaints of the same problem.  I took the internal mechanism out of my original one hoping to be able to fix it, but it couldn't be opened without destroying it.

This replacement has a different internal mechanism.  Seems to be a different mfr. and has a lot more metal in it rather than the all-plastic original.  Whether this one will last longer, only time will tell.