If you're the type who typically updates every year (or especially more frequently), JOD is awesome. I wish it was clear across the board; as it stands, only telesales and care can offer it outright to anyone. Stores only offer it for Smartpicks, or new customers that come back with an R rating.
A key selling point of JOD - besides the frequency of upgrading - is that well-qualified can walk out of the store (or off the phone, etc.) paying $0 down. Monthly is a little higher, and insurance is mandatory (because it's a leased phone)... but take where I am for example: tax rate out here is 10%. That's a large chunk of money that doesn't even count toward the financing. Add to that a $25 SIM, and you could be nearing $150 without putting a dent in your payment.
Putting more down is definitely an option, and the iPhone upgrade program should be available to you either way you choose to go.
Good luck! Hope everyone gets their phone(s) in 2017... lol