The synthetic brushes are made of Taklon which is a synthetic, non-animal fiber. Very soft and makeup application is easier and looks better on your face. The bristles are compact and not likely to shed like the goat hair brushes. With the synthetic bristles you may want to hold the brush straight versus holding it at an angle if you have powder you wish to apply. The soft bristles will make the swirl tap and buff process different. The soft bristles will make your powdered makeup seem like it's creamy. So as far as the swirl tap and buff application for the bare minerals original powder, the goat hair brushes will give you a faster application process. The soft bristle brushes are good for swirl tap and buff application, but I would rather do the tap and buff application with them if I want to apply my makeup faster and more evenly.
I have always used bare minerals natural brushes as well, and for that reason I was skeptical about purchasing this set. However, I would go for it if you are considering it. The synthetic brushes are just as good as the natural ones in terms of quality and makeup application. The main difference is the feel of the brushes: these synthetic brushes, of course, do not feel exactly like natural hair. They are a bit more shiny and silky, and the individual hairs are smoother. The difference is not that noticeable when you compare the eye brushes. However, you may notice a difference between the natural and synthetic face brushes, since the latter will have a slightly softer feel.