If someone wants an existing but offline only checklists app you can try mine: Fast Lists [0]. It includes options for nesting and hiding the already ticked items so it can be used with large lists.

I haven't added synchronisation yet as I'm not sure the return would be worth the time and I'm also concerned about conflict resolution and data loss.

The OP has a picture of a cockpit which would imply a safety critical environment. I would think long and hard before selling my app in that way especially for an online service.

[0] https://itunes.apple.com/app/fast-lists-checklists-for/id481...