I first figure out the phone. my Iphone 6 is not 4K its HD1080P. so anything above 1080 is a bonus. for the PC I use an editor, quicktime is needed on MOV not mp4 just the codecs and the editor normally supplies it. so @clionac has offered some info.
We still have no clue the win pc thing. Powerdirector for me works (Smiles)
Well, if it works without problems and you are satisfied with the possibilities/limitations of Quick then you can use it - why not.
For ambitious video editing I won't use Quick, only time I use Quick is to make a short slideshow of photos, which can be fast shared with other people.