A 650NK/650i is just a mediocre copy of a 2006 Kawasaki ER6N.
If you can find a 2nd hand low mileage one from 2006-2010 even the dumbest of the dumbest should realize it's a better bike than an NK for the same money.
Paid for positive reviews are a sad fact of life these days. Also how can you get any idea of the long term reliability of a bike from 400 miles ride or two?
You'd only buy a new NK if you were paranoid about 2nd hand bikes having been abused or you totally overvalue the idea of a warranty, that can actually be a PITA in the UK.