Nickle-Iron just like any other type of battery is not indestructible, nor is it totally tolerant of things that we can do to destroy them. My experience with NiFe batteries is strictly limited to some experiments that we performed on some old Thomas Edisons that we got from a remote cabin. They all were over 80 years old and all were able to be recovered, through following the instruction in a old Thomas Edison manual. Many of these were dry when we received them , and none of them would hold a load. Following the electrolyte replacement and charge discharge regime from the manual were able to be returned to useful cells. Oops almost forgot there was one cell that just would not recover. Since I was just using these as an experiment to see if NiFe cells followed the same aging rate as NiCad cells (1% deration per year) I utilized the IEEE 1106 fro NiCads as a guide for load testing. The results were published at Batton 2011. It was only talking about the Thomas Edison cells that I was working with, but the conclusion could be arrived a that when properly taken care of that technology can be relied on for a very long life as the internal normal aging/degradation is predictable.
If I was to be off grid and wanted my battery to last longer than I will be around, with what I know right now I would install a NiFe. However one question that comes to mind is "is the new NiFe as good as the old Edison's" I have no answer. And yes they are expensive. I would think that old NiCad's would last as long as well.
You mention Isoutar and I have not heard from him in some time. He is a good person that means well, maybe a little over aggressive in preaching what is environmentally responsible, but means well. and yes he is a flag waving, card carrying NiFe proponent.
I agree that NiFe's are not indestructible, nothing is. But to sort of insinuate that the technology is "??" due to actions on the part of the user is sort of like tossing a loaded shotgun into the back seat and it goes off and blows your arm off, and then blaming the gun manufacturer. Not a good comparison, but you can see what I am saying.
But you are correct they are not indestructible, nor do they not occasionally have some issues where cells will fail for whatever reason. See John's post about his three cells. If you think there are issues with NiFe cells, you might want to think about the issues that some are having with the "top of the line rolls stuff".