My experience with challengers, my opinion:
I buy trains to run them. If it runs quietly, pulls smoothly and is reasonable I'll buy it. My very first 0 scale purchase was a ignorant lot acquisition of four Williams Articulateds in 1994. Almost went back to gauge 1 brass they were so disappointing. Cab forwards were geared extremely slow like an old tired dog, the challenger gear boxes were so loud the neighbors complained. I believe they were powered by coffee grinders.
To make matters worse the importer started selling them out the back door for half of what I paid for them. Like trashy ladies of the evening, different customers get different prices.
So I dumped the Williams and picked up several smooth and quiet MTH big engines and all was well until I discovered Sunset. Sunset is the workingman's gold standard.
Great product, fair pricing, a runner and a looker plus the Mann family cares about their customers and Sunset will never have zinc rot.
Just opened my black box 2 rail Lionel GG-1 and the side frames were bowed out & disintegrated into black dust.
I did pick up some Oriental, Precision and Overland but not being skilled in brass soldering and painting I blew them out. They should be sold with a brass magnet to salvage the pieces which fall off.