I bought a used iPhone 5c about a month and a half ago because my old one had a small incident involving liquid that it shouldn't have touched. The used one worked just like my old one, however the battery—with the use of an app—was found to be very worn. the capacity was way behind, and the battery would often overheat.
The repair went very similar to the repair procedure, except for the adhesive strips that everyone else had a problem with. Probably would have helped if the rear of the phone was heated by something to expand the adhesive. But, regardless, the repair was still doable when the strip handles snapped. The battery is flexible, so just be careful and take the long spudger tool and slowly pry up on the battery. Do not put too much pressure on any of the internal components of the phone when attempting to get leverage. This will damage them or the brittle sidewall of the phone.
Heat up the back of the phone with either the solution from iFixit. Even a hairdryer might work. This might aid in the darn adhesive strip issue. But other than that, very straight forward, even with the ridiculous design of the iPhone's user-friendliness