Quick take
WF10 is rated for 1–3 bathrooms at 12 GPM. WF13 is rated for 4+ bathrooms at 20 GPM. Pick from real peak demand and pump capability, not tank diameter alone.
WF10
RKIN lists WF10 at 10 inches wide, 12 GPM and 1–3 bathrooms with 1-inch connections.
WF13
WF13 moves to a 13-inch tank and 20 GPM for 4+ bathrooms, also with 1-inch connections.
Why the bigger model is not automatically safer
Larger regenerating tanks can demand more backwash flow. An oversized filter on an undersized well pump can perform worse than a correctly sized smaller unit.
Choose from test results and flow together
Confirm iron, sulfur, manganese and pH first, then choose the smallest model that comfortably meets household and backwash flow needs.