I have not used Hydrofarm thermostats. However, if I understand correctly, they are on/off style, which can create much more extreme temp swings that a proportional tstat. Since you are already managing temp differences from top to bottom on a rack, I personally would not add another factor of instability. I only use on/offs for my QT tubs, since they are only running for a limited timeframe on a single enclosure. Spring for the Herpstat.