I am generally not a fan of carbon wheels on mountain or cross bikes. The risk of damaging them out weighs the benefits IMHO.

Having said that, I've looked into these wheels and they are quite light for the cost and carbon factor. So, if you want to go carbon, they seem like a good deal. They also claim to have reduced the likely hood of damage to the rim through some changes in how the rims are shaped.

I'm pretty sure you could get a really good (and nearly as light) pair of wheels with alloy rims for less money if you had custom wheels built if you wanted to upgrade later.

My 2 cents.