Best purchase
Pulse Grow Monitor. This thing let’s me know if lights are on/off when they shouldn’t be, temps get too high/low, and humidity spikes/drops. The pro model also notify me if my CO2 bottle runs put and does PPFD and spectral analysis.
Worst purchase
My original “blurple” LEDs. I think I paid $300 each for a 100w panel (advertised as 180W).