My iPhone battery started dying very quickly, i.e., wouldn't hold a charge for more than 1.5 hours while using or a few hours while not using at all. I kind of wanted a new phone anyway so I ordered an SE and decided to use this as my backup. So it gave me some time to figure out how I was going to deal with the battery problem.
I was planning to do the repair while in the company of my father, who has some experience repairing small electronics. I ended up doing it by myself, but it went ok. I took a break while working on it because my hands started shaking.
I didn't have any real problems using the suction cup that comes with the basic repair tools to open the phone. However, it was a little nerve-wracking because I was concerned about tearing the Touch ID cable.
The adhesive strips tore right at the outset even though I was trying very hard to be careful. Getting the old battery out was definitely the hardest part and I almost decided to give up. I used a combination of a hair dryer, plastic card that I don't care about, and dental floss to finally get it out. Possibly what made it more difficult was that I hadn't disconnected the battery yet. Whoops. Don't forget that step.
I will also say that the #000 Phillips head that came with my repair kit was too small. I had to put a LOT of force in to unscrew the interior screws before I realized the problem. Thankfully a larger Phillips screwdriver I bought a few months ago saved the day. The two screwdriver heads are labeled the same size but they are obviously different.
I would say purchasing the iSclack would be worth not having to deal with the worry of tearing the Touch ID cable. But if you're using the suction that comes with the basic kit, just try to not use too much force. You're not trying to pry up the entire screen, but rather enough to wedge the spudger into the bottom left corner. Then work your way around to open it up.
You will have to fold the battery cable. There isn't a step that shows this, but the cable isn't supposed to sit on top of the battery, but rather beside it. I didn't realize this at first and was trying to pop the phone back together. I wouldn't go because the cable was sitting on top of the battery. Cue panic and then backtracking a few steps to fold the strip, which was now more tricky because it already had a few kinks in it. Don't make that same mistake. In fact, I would recommend doing a test connection before you put the adhesive strips on the battery.
If you have a tempered glass screen protector, have a new one ready to go in case it breaks when you're trying to remove it.