My parents (both late 60s) split time between a co-op in Manhattan and a condo in Naples. Combined estate is ~$12M. If they die as New York domiciliaries, the NY estate tax on a $12M estate is roughly $1.1M (the cliff kicks in because they're over 105% of the exemption).
If they establish Florida domicile: $0 state estate tax. Zero.
The savings seem obvious but I've heard horror stories about New York challenging domicile changes. Does anyone have experience with this? What's the checklist to make it bulletproof?