I just bought one last week, and I too don't (currently) need all 4 Thermostats, but certainly will in the near future though. I currently am using 2 of the 4 for 2 different racks, and the 3rd I'm using to auto turn the lights on/off each day, and simulate sunrise & sunset (The BP's could care less, but I thinks it's awesome! I figure if I have the empty plug-in available before I get more racks, why not use it, right?!).
I highly recomend it. In fact, spend the extra $5 and get the Blue LCD
I wrote a bit about it here