Sonia G Soft Cheek Brush is a brush.
Soft Cheek Brush is supposed to give "sheer to medium coverage" with a slew of cheek products, up to and including setting and finishing powders. It fluffs up a decent amount after washing, which gives the edge a softer, more feathery feel and gives a more diffused applicator of cheek products. It has an incredibly silky-smooth feel but still picks up product well and can spread/diffuse them on my skin.
I liked it with softer powder blushes and bronzers and more pigmented, denser powder products but would use something else for denser, more sheer to medium coverage powders (which I'd use a denser, flatter-edged brush for). The overall brush head is longer than the average blush brush, so if you're someone who struggles to be lighter handed, that built-in length might be useful.