NN/g: split buttons unreliable on touch (fat-finger conflicts) — use sequential menus or accordions on mobile

Claim: Per NN/g's mobile-navigation research, split buttons for navigation (where part of the button navigates and part expands a sub-menu) are unreliable on touchscreens due to fat-finger conflicts — users frequently hit the wrong half. The safer mobile patterns are sequential menus (each level replaces the previous) and accordions (expand-in-place).

Source: NN/g mobile navigation research (foundational guidance, current 2023-2026).

Confidence: Industry-consensus.

Caveat from the brief's honest-gaps section: Mobile navigation patterns for multi-vertical service businesses specifically are underexplored in current research. NN/g's mobile mobile-subnavigation guidance applies, but no recent (2024-2026) study tests multi-vertical service-business mobile nav directly. Use the NN/g principles; don't pretend there's field data specific to this case.

The safe pattern: desktop mega menu + mobile accordion, not a single nav pattern across breakpoints. See NN/g: "On large screens, don't cover the entire screen when megamenus are open" (Apr 30 2023) for the desktop side.