If you use the kit you will invalidate the warranty . I replaced my screen from a kit. I'm very good with my hands but it was still tricky and the home button was never quite right. I wold NOT recommend it
Replacement screens are fiddly but the YouTube instructions v good - just watch out for aerial - had my screen replaced in a shop & they mucked it up but I didn't know until I'd charged it & couldn't get a phone signal . Then had to do a DIY job to fix it.
Handy tip.. I kept using my iphone for 6 months with a badly cracked screen by keeping it covered in cling film - worked perfectly & didn't get any worse.