I’ve bought some Digital Codes from TCG Loot page.
I can say Digital Codes are totally safe, you buy an item, go to a page and select Region/Realm and exchange the Code at Booty Bay.
I haven’t bought any from other sources though, so I cannot help you there.
I bought something cheap from them once to see if it was reliable. I can’t even remember what it was but I could instantly claim the code they gave me.