ECC doesn't typically yield that much of an advantage in the nominal case until you get into very large amounts of memory - it's just a more expensive part. I think it was calculated that cosmic rays are likely to cause single bit errors in systems of 8GB of memory only once a decade, and most embedded ARM situations (also carefully avoiding the "p" word) have far less than 8GB of memory. So if single-bit errors are causing your embedded device to crash, it's okay, it'll just roll over and restart... once every 50 years...