Well, just to think about this rationally: refurbs are either reconditioned used devices or returned devices. Why are they returned?
In many (most?) cases they are returned because the purchaser changed their mind, didn't like it, preferred something else, in which case there is nothing wrong with the device and it is equivalent to new.
In some (few?) cases it could be because there was something not quite right or outright defective with the device, and Apple presumably either tested or repaired it. In which case it may not be exactly equivalent to new.
I think we need to recognize the possibility of the latter. The associated risk rather depends on the device, IMO. I think the risk is small for most Apple devices.
But for some products, I think the risk can be high. For example, interchangeable camera lenses. There is significant variation in quality from one lens to the next (sharpness, alignment, etc). Many returned lenses are poorer quality copies - all within manufacturer specs, but some are just better than others. I never buy refurb lenses, not to save 10%. I would never buy a refurb printer, for another example.
My point is: it is not as simple as refurb sucks or refurb is great. Pick carefully what you buy refurb.
