Yes, R2 is now offering a lighter, better balanced power harrow, but it is still very heavy and very expensive versus a tiller. I've been asking Joel to offer a rear roller for the Grillo rototiller for a while now. If we had a rear roller, it would be almost as good as a power harrow, but much lighter and much less expensive.
I bought a rear mount power harrow for the fact that it does not invert the soil profile, does not pull up weed seeds to the surface, and it makes a fantastic seed bed. Since it is 3point mounted, I don't have the issue of weight. When you get to 13 foot models, the cost of a power harrow versus a rototiller is the same, so I don't have the issue of cost. At that scale, a power harrow makes sense. As a walk-behind tractor attachment, it is very difficult to justify.
On a side note - I see Cub Cadet now offers a power harrow.