The term refurb or re-manufactured
covers a lot of ground depending on which vendor uses it.
eg. open box, lightly used but undamaged and re-inspected, beta units upgraded to release product status, demos re-QA'd and repaired if necessary, factory test units (therefore not new even tho never sold), RMAs repaired, etc etc and of course customer leased used beat-up units repaired if necessary and re-QA'd.
Factory re-mfg or refurbs are at the top of the food chain and for recent products it usually means they never left the mfr ownership or oem factory before being marked for sale as refurb. Most of these can even be upgraded to 3-yr mfr warranty, but inquire prior to ordering the unit.
Experience? All factory refurbs I have encountered have never failed compared to new which sometimes need repairs or recalls.