I posted this in another thread last week or so but I've used both Steve's LED's and a DIY solution from Rapid LED on both of our 29 gallon bio cubes. Both kept whatever we threw in the tank. Easiest way to say it is like this:
1. Steve's LED's is a kit and comes in at about 80 - 90% complete. They already did some of the heavy lifting and all I had to do was remove the lid, unscrew the cover, gut it, and then insert. I think very little soldering was required. The heat sink wasn't bad, square tube but had a pretty solid fan that he sourced from a bin that Sony also used on their LED panels. So it flowed air. The 4 channel driver I recall he used does get hot and that is the primary source of the heat. You can swap out the bio cubes default fans, most of us with older 29 gallons already did that anyway, and you can have one pull in air, other side vent out, mixed with Steve's LED's fan cooling should not be a issue. Was not for me. Please note that I had a controller used with mind, Reef Angel, so can't speak for his things. It connected in easy and I had all sorts of custom lighting going on with ramp up, down, clouds, storms, etc.
2. Rapid LED DIY - I did all the heavy lifting, soldering, wire, etc. Meanwell drivers, power brick, and color/spectrum choice. I used a heavier and thicker heatsink so didn't have issues although I did the same as I did with Steve's kit by keeping the fans I upgraded to with push/pull design and it helped vent. This did not have a controller, just potentiometer, to control spectrum and intensity. Again, worked for us.
Both kept any coral we wanted. Neither had heat issues. Neither had condensation / water issues. Steve's was a bit more, a lot rather, blue spectrum so I found myself turning that down a bit. The kit I made from Rapid was more evenly split 50/50. Both kept SPS, LPS, and RBTA's. Both tanks got merged into a 40 breeder due to the RBTA's splitting and outgrowing the cubes. Later donated the cubes and upgraded the 40 to the 210 gallon I have now.
Steve's is a good source and probably less work. I don't think you can go wrong with either retrofit and I've had great support from both. I've used Steve's later on another project with his 8LDD board and pwm converter. Again, solid support and always in a timely manor.
Best of luck.