I installed folding aluminum mast steps on my Passage 42 back in 1992, just up to about four feet higher than the first set of spreaders. I use them to climb up to the spreaders to look for passages through coral heads and passes. I can't remember who manufactured them--maybe ABI, but they were spendy. About $20 apiece, I think.
I have been up and down them innumerable times, and they function fine. Care must be taken when installing them, so as to not drill through the mast into a wire or halyard run. I carefully ground down the inside ends of the s.s. mounting screws so they wouldn't grab the internal halyards, and also so they didn't protrude too far into the mast. And also the usual anti-seize compound between the stainless and aluminum. They make no noise, and I have never experienced any line fouling.
I also heard anecdotal stories of failures, but have not experienced any problems. I use the usual "three-point" care when climbing or descending on them, so if one of them fails, I have two solid attachments to the mast with feet or hands.
I wouldn't hesitate to recommend them. They make it so easy to scurry up the mast that I have often done just that to get a look at something in the distance or just to enjoy the view.
They weigh so little that weight is not a consideration. And they really create no additional windage since you can fold them closed as you descend.