Yeah!! it's the default watercolour brush in SAI by virtue of it being uh, the only brush I use haha. I'm terrified (probably without good cause) of becoming reliant on a specific custom brush or precise combination of settings I could somehow "Lose" - SAI is such an easy program to acquire a copy of on any machine and knowing that my copy is "ready to go" as soon as it boots from factory default is something I appreciate. It is genuinely just everything I want out of a brush though - versatile, simple etc.
I think that owes more to SAI's blending engine than any unique feature the brush itself possesses - SAI feels unlike any other program i've tried and that natural, intuitive blending is the chief reason why i'll likely never use another program unless i'm forced to. I'm a "if it ain't broke" bitch in most aspects of my life!