This is the brush I have used for its price, and it is underpriced for its quality.
The softest synthetic powder brush I have ever used is by La Mer; the Sephora Pro #91 followed by the IT Cosmetics Heavenly Luxe and Too Faced are nice, but for the price and marketing, are nowhere close to the La Mer. Ecotools is just scratchy, and the Sonia Kashuk was more firm and dense than I was looking for. I have sensitive skin and I hate the feeling of my brushes stabbing my face. Because I do not feel comfortable testing store brushes on my face, I brush them against the part of my wrist closest to my ulnar artery. This is the most sensitive part of my arm. If the bristles are too firm, you will definitely be able to tell!
I use this to re-apply my sunscreen and freshen up my makeup, Mary Philips (via Melissa Alatorre)-style. The bristles are soft, fluffy, full, yet not dense like an Artis brush. It stands up to liquid products and frequent rough re-washings, and I do not doubt its abilities for powder.
Best $9 I have ever spent, but if my husband does decide to gift me the La Mer brush, I will relegate this brush to travel.