It works if you only allow incoming calls from your contacts (e.g. whitelisted numbers) on friends/family/work line. If that number leaks, who cares? The random numbers will be blocked anyway. Probably would want to set it up so the 'public' line is silenced - just periodically check the VM box for anything important.

It seems possible, but maybe not affordable, for scammers to buy information about you and then spoof numbers of places that could/should theoretically call you. If you couple this with the potential victims on the other end being elderly you've greatly increased the risks of the attack being successful.

But then you're right back where you started: When you need a clean number for a hospital or similarly important service to call (Wife's work, daycare, school office), it goes to the distrusted, silent-by-default line, or, just as bad, it doesn't ring the clean, only-whitelsisted-numbers-ring line