Late to the party ...
I think its a waste of money, but ...
Wifee and I started with Model-S in 2015 and add had a 3, since replaced with Y, and a replacement S in the interim.
The S has a fob, and Wifee has one (buried in her handbag) for the 3. I use my phone.
I've never had any delay opening a door with my phone-as-key. I have to remember to grab the fob if I'm going out in the S (I can unlock the S with the APP, and also enable "drive" - if I lost my fob.)
I carry a wallet, so I have the card-key in there (and Wifee in her handbag), can't remember the last time I used it ... but if phone had a flat battery I'd be able to.
I have a Tesla wall charger, so don't need the "release charger" fob button.
I might use Fob if I had an armful of groceries, and had the fob in my hand so I could press the fob-boot-button when I got close. But, me being me, the fob would still be in my pocket rather than my hand, so no use in that situation ... I've still have to balance groceries precariously whilst reaching for the boot-handle ...
Hopefully you mileage will be better