I got 2 Zetlight UFO's with my 75g FOWLR when I bought it from a co-worker that was moving and did not want to keep the tank through the relocation. They were "worth it" for me since I got them along with the entire system and several fish for an overall cheap price.
They seem like pretty good lights, but I have not measured PAR and have not grown any significant corals under them yet to prove how good they are. I just recently added them on my 40B on my work desk.
In general, I feel like the Zetlights are a bit overpriced for what they are. The program for different lighting at different time of day is nice. They are not the brightest lights for the cost, but they are not the worst.
Both pictures are fairly true to eye-view.
40g Breeder tank with only UFO's, running day program near max blue, white, UV, and 50% reds:
Same as before, except also including a relatively-cheap Hygger light (primarily white light with a bit of blue/red/green) since I prefer more full-spectrum light than primarily blue: