This article is from the Fitness FAQ, by Jeff Gleixner (firstname.lastname@example.org) with numerous contributions by others.
Last year, I spent just under a hundred dollars on one of those
"cheap" stair climbers at Target. The center linkage broke with just
a few weeks of only moderate usage. I repaired it myself and it
broke again and again and again. Finally, I installed a number
fifty roller chain and a stainless steel sprocket mechanism of
my own design. This worked wonderfully until one of the shock
absorber things broke. I gave up at this point.
When it was working, the stair climber gave me sore knees constantly.