I thought some people might find it interesting to know that there’s a website which lets you scan trainer codes with the QR code scanner, which makes it really fast if you’re looking to mass-add friends for gift sending/receiving! The website is http://pokemon-go.yellowbumble.be/ if anyone is interested 
I originally saw the post on Reddit, so maybe other people have also tried it out already!
That would be great if you are wanting to add just random codes for friends.
But I prefer the codes posted here in the hub as they provide at least some info regarding the players like from where they are, their reason for posting their codes and some with their In-Game Name, at least some level of filtering is implemented.
I think it would be more useful for newer players, or for people who send 100+ gifts a day which you can specify when you add your code. If you’re looking specifically for certain locations for achievements or eggs then yeah another method is probably better, but it looks to be pretty good for mass-friending or mass gift opening/sending.