Like Quantum, I have insufficient experience with LED, but I will say that there are LED fixtures available today which are fine over planted tanks. You have to know what you are getting, and they are initially much more expensive, but long-term savings are significant.
Having said that, the blurb at the linked site says this fixture is equivalent to T5 HO. If this is true, this might work well.
T5 HO is more intense (brighter) light than regular T8 or T5 NO when comparing the same type and size tubes. So that being said, a 24-inch T5 HO might work, similar to a 36-inch T8. And if that is true, then likely the linked fixture would work.
If this were me, I would want to buy this from a local store so I could take it back; not knowing what I'm getting, I would want to try it over the tank. I did this with the T5 HO, for a week, and returned it for a T8 because the T5 was far too much light.
On the length issue, I don't have problems with tubes shorter than the tank length, depending upon their intensity. Over my 5-foot 115g I have two 4-foot T8 tubes and this is fine. And with the above, we are talking much brighter light to begin with, so this might not be an issue. But again, this is surmise, since I do not know this fixture.