We were recommended it by the guy doing the timber framing (a rather mad Canadian, but a fantastic worker). It was mostly done for speed and it also allowed us to have an extra four inches on each outside wall by not having a block outside.
Having said that, the plasterers were a nightmare, but since you won't be doing that, you will save that pain!
I haven't seen blocks on a TF house, so I don't actually know how it compares! If you are in a site in a field like us, then soundproofing isn't an issue (and anyway you will have the stone facing), it has the same insulation properties as a block layer (i.e. not much! about 4 inches of rockwool equivalent, I believe), and I believe it is now certified for use in Ireland (it wasn't when we used it).
The actual board went up in about a day and a half, but the plastering took a few weeks (more to do with the plasterers and the weather than the thing itself).
HTH, Eoghan.