I haven't specifically ordered an iphone display from ifixit but I do see their parts come through my door on a fairly regular basis. I'm nosey so whenever I see a part I work it over to see what I can determine about quality, I haven't seen any quality issues with their parts.
What I DO know, is ebay parts. Its a general statement but as a rule, there are no quality displays being sold on ebay. Even a blind squirrel finds a nut occasionally but general flow of where parts come from is something similar to this;
A factory in China manufactures them or parts are refurbished either here or there. These are sorted by quality and sold in huge bulk to wholesalers. Wholesalers get them and are essentially a middle man. They're sorted again and are sold to either another middle man that looks to sell them in small quantities (ebay, amazon, etc.) or sold in chunks to shops. Shops put their name on their repairs, they GENERALLY want quality parts (there are exceptions that look for the cheapest) and are willing to pay a premium for that. The good parts go there.
Super inexpensive (and they're inexpensive because of quality) wind up on ebay being sold one at a time to people that don't do this every day and as a result aren't able to pick out whats a high copy, refurb, apple original, from a b stock cheap steaming pile of mess.
Go with a reputable source, look for a source that offers a warranty on their products, one that isn't going to disappear tomorrow (how long they've been around is a good indication)
Right now the prices of iphone 5, 5c, and 5s displays are up. Way up. nobody is getting $28 dollar screens right now, its just not in the market at the moment