Aftermarket grips for the VP9 give you texture that holds reliably under recoil and sweat, geometry tuned to your palm rather than an average, and a thumb shelf for fixed lateral control on every draw. The VP9 factory frame is ergonomically well-shaped; aftermarket grips go beyond that for the shooter who wants hand position to be completely consistent and not just approximately right. The VP9 and SFP9 are the same platform -- grip compatibility is the same.
Confirm compatibility on the individual product page before ordering.