I have had a current USA Sundial fixture for the past 18 months and I like it. I have the 48" model 4X54W on my 55G mixed reef.
I bought this fixture when I was first starting my reef because is seemed so much simpler than other alternatives. I really appreciate the built in timers and moon lights.
I have LPS that are doing great and SPS in the top 1/3 of the tank. I have not tried a clam yet but I am thinking about it. About 12 months ago I upgraded the stock bulbs and I would strongly suggest that you do the same.
I am happy with the lights, but like most things in this hobby, I sometimes dream about going bigger, better, stronger.
Hope that helps.