There are other similar products like Liquid Armor that offer this type of protection. There was also a recent crowd funding project (Puracoat on Indiegogo) that offered to do the same thing. I bought into the Puracoat and it seems to work on my Moto X (2013) and I have applied it to my wife's N4. It seems to work pretty well but it does not prevent finger prints or smudges as stated. You will still get smudges and need to wipe it daily. I haven't tried to runs keys over the phone but so far it works pretty well on my end for my wife and myself's daily use.
EDIT: I've purchased a Note 4 for myself as well and I'm waiting for my cases to come in before I start using it but I have already applied the Puracoat to that phone as well and will have a better gauge as to how well it holds up once I get it up and running as my daily phone. I have some film screen protectors at home already so just waiting to see how the Puracoat performs (hopefully it won't be too late by the time I need/want to apply a screen protector).