The brush hairs in full size and the sets are the same, the only difference is the full size are man made, and the sets are machine made.
The first negative I always hear is the brushes are scratchy. When machine made, there is a little more room for error, so some bristles might go in backwards. With face brushes, if a few bristles are in backwards, it won't make a difference, but with eye brushes, that can affect the feel.
I have both version of the 187 brush and I love them both! I can't tell a difference in feel or performance. And if you look close enough, you will notice there are more backwards bristles in the full size brush! I actually use the small set brush more because I like the short handle, so the bristles have spread out a bit more, but that is purely due the amount of use. The face brushes, which are most expensive, make the sets a great value and the quality is pretty much the same as full size!
With this 239 shadow brush, there is a slight difference in width, but nothing that affects the performance of the brush. There is only one type of bristle and since there is very little tapering at the sides, a backwards bristle won't affect the performance. From the side the thickness is pretty much the same:
Now the only time I think the set brushes are not good are when it comes to small eye brushes that are tapered, like the pencil brush or the angled brush:
This one is a 266 brush and it is useless. The bristles have started shedding and coming out and the tapering is not even.
Ladies, if you want the brush sets mostly for the face brushes, go for it! If you want the specialty eye brushes, save up for the full size. This makes the most sense too because the face brushes are more expensive and a better value to get the kits, and the specialty eye brushes are cheaper so you don't feel as bad buying the full size ones.
What do you think?