F20/SS134 is Sigma's large short-handled paddle brush. It's their dupe for the MAC 134. I don't own the MAC one, but I definitely like the Sigma one. I like that it's short-handled, sort of travel sized. It fits perfectly in my makeup bag and is great for on the go. It's basically a powder brush, but flat, so you can use it for applying bronzer or powder. The Sigma website describes this brush as "Large paddle-shaped brush with fluffy and rounded tip. Suitable for application of powder products on face or body. Natural fiber bristles"
Anyway, I would definitely recommend this brush, it's very soft, does not shed and is short handled, which I like. You can check it out on the Sigma website here.