I have 2 52 HDs. They're beautiful lights, easy to set up and run quiet and cool. Dialing them in has been a pain. I've used a PAR meter many times and seem to get inconsistent readings for the same spots. I'll ramp up the wattage and yet the PAR decreases, and vice versa.
On my new build, I'm keeping the 52s, adding a third and then also adding T5s for growth. I feel like I never got the quality growth out of easy SPS (slimers, birdsnest, etc) with the 52s. Great for fluorescence and cool features like the ramp effect and moonlight, but LEDS...not sure they are all they are cracked up to be IMO.