Article has a nice summary of the differences between standard and in-band ECC. Looks kinda like the difference between hardware and software RAID?
In-band ECC trades performance for resilience because by allocating some of your memory bandwidth to checksums. This is dramatically simpler, and thus less expensive, than traditional side band ECC, which adds a redundant memory channel dedicated to parity information.
Seems like a hugely valuable option to me. Needs more OS support (Intel says ChromeOS only for now??). Would be interesting to compare price/performance/resilience against used/low end server hardware.