Yes and no. Mathematically it is the same, which is why I'm not even going to argue; it's a great way to get your phone if you don't want to pay it all up front. That also assumes you are going to keep/want to keep it. It is very easy to fall into the cycle of being on Next paying $786 (128 GB 6+ pricing over 24 months) total on your phone at the 18 month mark, then wondering if it is even worth it to pay the remaining ~$300 to buy it off AT&T. It would probably make more sense to just trade it in at that point and get the next phone; continuing the cycle. Plus, it keeps you tethered to AT&T's network discouraging you from leaving as you'll have to pay the lump sum to buy the phone, or just lose that $786 you've dumped into it. It's a mind game that I wouldn't want to get into, and don't plan on doing so. T-Mobile's Jump on Demand program that lets you upgrade 3 times every 12 months is even more brilliant.
If you're the kind of person that doesn't care about actually owning the phones, and wants a new one every 12, 18, or 24 months then it's brilliant. Or, if you're like my wife and you keep the phone until it dies, then it is also a brilliant idea as you can pay it off slowly with no interest. But, I just don't want to get involved with the mind games and like the feeling of paying for my stuff in full when I can. Certain items (like a house) are difficult to pay for up front, but I aim to make my phone purchase a "one and done" affair.