I had my cracked iPhone 6 screen replaced. Cost was approx $115. When I got my phone, I compared it to another iPhone and saw it was significantly darker. Also, there was a small hole that was projecting white led light. I returned the phone and was told it was aftermarket parts.
In the end, the guy gave me a new screen and the phone looks great. However, I think they use cheap or low quality replacement parts. Second, customer service and quality assurance is poor. The guy/owner was not friendly and was not apologetic. In hindsight, I would have went to the Apple Store.