If the used WDH was properly utilized by the prior owner and there isn't any visible degrade of mating and/or moving components (friction pads, metal-on-metal parts, etc.), IMO it should function as good as a new WDH of the same make/model.
With any WDH, used or new proper sizing, installation, and adjustment are key in optimizing the designed performance of the WDH.
My WDH is over 10 years old and performing just fine.
Bob
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2016 GM 2500HD 6.0L/4.10
2018 Jay Flight 24RBS
2002 GM 2500HD 6.0L/4:10 (retired)
2005 Jayco Eagle 278FBS (retired)
1999 Jayco Eagle 246FB (retired)
Reese HP Dual Cam (Strait-Line)