I do have to rely on mine in the spring when I have 20 or so flats of tender transplants in the GH. A bit of chill will not hurt them, but overheat once and they're toast.
Bayliss cost a bit more but they are the highest quality materials and craftsmanship I've found. When I worked in commercial GHs I learned the best system overall was a polytube ventilation system using a thermostatically controlled louver. I have been looking for the materials I need to assemble one on the scale I need (difficult). Since I run fans 24/7 the operating cost would not change that much. The poly tube causes a constant even flow of air throughout, the louvers open at a preset temp, and lastly an exhaust fan or vent opens later as needed.
