3 for 3- new batteries in our families iPhone 6 phones.
My family isn't ready to upgrade to a new phone yet, however all of us have iPhone 6 phones that we got when they first came out. Funny, all 3 phones started having battery issues in the last couple of months. 3 years - I guess that's the limit on the OEM battery. I knew that iFixit would have a battery replacement guide. So I ordered 3 batteries and a set of tools from iFixit. I also knew that Apple would have done this replacement but I got all 3 replaced for the cost of one Apple replacement.
The repair went very smoothly, only issues I had was not unexpected.. the pull strips on one phone broke, Not the end of the world, I knew just a little more work to get it out. One other thing, I didn't remove the screen or the cables to the front as directed in the repair instructions, I did carefully support the front and the flex cables during the battery removal and insertion process. I'd say unless you are all thumbs, this is a pretty easy repair with the tool kit from iFixit.
As I stated above, the removal of the front wasn't necessary if you are extremely careful with the support of the front while you remove and replace the battery.
The pentalobe screwdriver was of higher quality than I expected that was a pleasant surprise, so I can recommend the iFixit tool kit without reservation