It's going to be hard to tell without PAR data. I have a Beamswork fixture on a tank half the size, 1 inch shorter. It has a total of 54 LEDs, at .2W. This has 30 leds at .5w. So, my fixture, which is half the size, can grow far more than you want but isn't that far from low light. I would think one fixture, which when you double the tank width, would be about 2/3 the wattage I have. It could work for your needs. That comparison is making a lot of assumptions. What is nice about these, and other Aquaticlife fixtures is that if it's not working for you, add another.
At the clearance price, it is likely worthwhile. However, I would buy 2 minimum. The other issue is if they sell out at the clearance and you do need more, that may not be the best choice as they seem to go for $60-80 elsewhere.
My post is all speculative but in my research, it seems lower wattage LED's tend to be more equivalent to higher wattage LED's from fixture to fixture.