Designing to remain robust in the face of failures is compulsory for any project of any significance. Or at least it should be, though a lot of projects go on a wing and a prayer that nothing will go awry and "save" those engineering hours until a catastrophe at some future point. It basically just prioritized what already should be a priority.

I have no doubt that fringe/niche instances have more competitive spot behaviors, though how you set your bid range dramatically impacts how you survive through competition, but I had vanilla instances last for literal years (note that by default the spot requisition has a lifespan of one year so you have to modify that) at per hour pricing somewhere in the range of 1/5th on demand.

But mileage will vary.

I don't use those spot instances anymore as my projects are much better financed now, and I have significant compute on other platforms including bare metal in colocation facilities. However when I did I stayed silent about it, feeling almost like it was a secret that would be ruined if others knew about it.