Something I have heard people talk about with these (I have not personally researched any of this), is that LED's have a life span just as halides do. I would try and ascertain what that life span is roughly as well as the cost of replacing an LED array and include those numbers in any kind of maintenance cost analysis. Also, last I had heard, these things just didn't produce the kind of PAR you can achieve with MH.
Again, these are not things I have looked into myself, just second hand musings. But, these are the first things I would look into were I interested in these LED fixtures... FWIW