One of my makeup philosophies are, you can own all the makeup in the world, but if you do not have the right tools, it does not matter how much makeup you own. Often times, people underestimate the power of brushes and how an impeccable brush can truly make a world of difference in their makeup application.
When it comes to eye shadow blending, I only use the MAC #217. There are many eye shadow blending brushes that resemble this brush, with its dome shape and fluffy bristles. However, there is nothing that compares to it (trust me, I have been open minded and have tried many others)! I literally own about ten of these brushes in total between my professional makeup kit and my own personal use.
Eye shadow blending is definitely an advanced skill set and by that I mean it takes time to really master the art of blending. It is for this reason, I highly advise picking up the MAC #217 brush if you want to step up your makeup skills and really be able to blend eye shadow more proficiently. This is not only a makeup artist necessity but I personally cannot live without it!