Just to add another data point, our startup uses Gusto and my salary isn't in the data. My old salary from Google (which I think used ADP) is though.

"Do you agree to allow your data to be shared with 3rd parties as necessary to provide you with the best service possible?"

[races off to something much worse than you imagined with your data]

Three-person company here. We do our own payroll, using Quickbooks (not their payroll processing service, just Quickbooks the desktop application). We have employees in two states.