+0.5 and blacks position is not bad, im surprised the butcher did not mention this
i much rather play 6.be7, the point being, in the line you mentioned,if black plays c5 and white plays d5 like in the line you showed. black plays na6-nc7. exd5 so soon is not that pretty.
What is the big point behind 9...b4 other than exposing Black's queenside? Probably a matter of taste, but 10.Na4 looks very natural, and strong to me.