Personally I went with amazon as I needed it quick and got 2 day shipping on it through amazon prime. Ebay if those work as promised is not bad. But I personally would get an actual Delta or Sanyo.
The way I see it is why risk a miner for a few bucks on generic fan. That is unless it's very old miner and you don't really care. But S4 still has some value.
You are absolutely right about the quality level.
There is a quote about it: I am not so rich to buy cheap things)
Of course cheaper fans will go out of service faster..actually its a lottery with the brand fans too, but chances are higher)
I downclocked the s4 for stable temps and searching for some eu-based seller to have the fans in shorter terms then from us or china.
But actualy it depends on seller and the delivery type. I used to receive a Bitmain warranty replacement PSU within a week from china to Eastern Europe by UPS.