My iPhone 6 battery was giving me less than an hour of uptime on 100% charge
This was the toughest repair I've done yet on an Apple product. I've done various jobs on Macs, iPods, and older iPhones. The disassembly and orientation inside the device is quite easy, but heaven help you if you break one or both of those adhesive strips. I broke both and getting the battery out was a nightmare. After countless strands of snapped dental floss, the constant whirring of a hair dryer, deformed credit cards, and a slightly bent battery it finally came loose. After all that, reassembly was fine and the phone worked perfectly.
It might be worth getting the iFixit pry card just in case. I wish I had it. Also, watch the separate video on removing the adhesive strips. It shows the process in a lot more detail than the general repair video does. I don't think I stretched mine nearly far enough and wish I had seen that video before I attempted the removal.
Also, YMMV, but I barely pulled on the screen with the suction cup and the bottom freed up enough for me to use the pry tool the rest of the way. I'd recommend doing it this way if you can, rather than applying a lot of force to the glass.