An app tested in the office on stable WiFi will feel smooth. The same app in a field, a concrete warehouse, or on an inter-city road can turn out to be useless.
Offline-first isn't a feature you bolt on later. It's an architectural decision: data is written to local storage first, the interface responds immediately, sync follows once the network returns.
The hardest part isn't storing data locally, it's resolving conflicts. Two officers edit the same record while both are offline. Who wins? The answer is a business rule, not a technical one, and it has to be decided with the client upfront.
One habit that always pays off: test on location, with the actual phones officers use. A low-end device with nearly full storage will surface problems that never show up in an emulator.