All went well for me, but I didn't replace either set of adhesives (battery or back panel). I figure the battery will be fine without it, and the old adhesive on the back panel was more than enough to re-adhere. With the phone in a case anyway, it's perfectly fine. The trade-off for being able to more easily replace the battery again is losing waterproofing, but I've never dropped a phone in water and don't plan to start now. And I doubt the very generic battery supplied in this kit (without any manufacturing date) will last a year.

I don't know how unusual my phone was, but I'm surprised at the number of reports of back panel breakages. Once the back is warm enough, all the resistance of the glue disappears and you don't need to apply much force through the suction cup at all. Just have patience, keep warming the edges, and although it takes a long time you'll instantly feel it when you get there.

I also struggled with this, and I recommend just not using anything at all but just putting the new battery in and closing it all back up. The tolerances in construction are very fine, and there's no way that battery is moving anywhere once the NFC coil and back are replaced. (Would be good to know if I'm missing something here, though?)

(As annoying as all the stupid glue was, you have to admire Samsung's build quality here -- it's a very well-made phone inside, and there's not a fraction of a mm to spare.)

I really struggled with this step. The iOpener provided burst when heating up for this stage, so I ended up using 75°C water in a small-but-strong ziplock bag (I first tried hot water from the tap, but that wasn't warm enough). Not ideal, but I had no other option available. Samsung had used a lot of glue under the battery, and it's not something you want to force with a spudger. I did get there eventually, but it was pretty unpleasant trying to avoid puncturing a potentially explosive battery.

I did not replace the glue when installing the new battery; it seems pretty well held in place without glue, and there's no way I want to go through that process again.

Removing the back wasn't too difficult on my phone: several rounds of heating with the iOpener, applying gentle pressure with the suction cup, and eventually a corner lifted up without much force and I could easily slide a pick in. From there it was very straightforward and I had no trouble sliding the picks around and removing the back. The battery removal was much harder in comparison (especially as the iOpener burst when reheating in the microwave for the battery, despite following the time instructions).