I don't doubt that it's usable in the areas where Apple cares to make it so.
But as the comments make clear, it's all about the number of 9s in the reliability. If they're 99.9% reliable, that means 1 out of 1000 data points are wrong. You will definitely hit a wrong one. If it's 99.9999%, then it's 1 out of 1,000,000. You might not. Adding those last few 9s are incredibly costly.
But as the comments make clear, it's all about the number of 9s in the reliability. If they're 99.9% reliable, that means 1 out of 1000 data points are wrong. You will definitely hit a wrong one. If it's 99.9999%, then it's 1 out of 1,000,000. You might not. Adding those last few 9s are incredibly costly.