If you are going to use a Herpstat Pro or 4 to run multiple racks or enclosures, keep this in mind, the temp probe leads that come with the unit are 6 ft. long. So, unless you can position all four racks or enclosures within 6 ft. of the base unit, you may need to order some of the 12 ft. probe extensions to reach everything.

I use a Herpstat Pro.