Go for it! I bought a 2003 Colnago Asso from Sierra almost two years ago and it was the best thing I bought in my life! You do not need to worry about this vendor, they have an LL bean return policy.
Only issue might be that for the colnago warranty to be in effect it has to be assembled by a colnago dealer.
I bought a full bike and I didn't worry about it--I got the complete bike for $1,250! That's less then 1/2 price.