SD Flash will die pretty quick if you continuously write to it, like for a blockchain database.
So ok for backup, but not really for a node.
As long as you can limit your erase/write cycles, this analysis earlier in the thread suggests it should work:
We aren't talking about using a SD card for RAM. The SD card would be used to store the blockchain, update the blockchain with new blocks, update the unspent outputs each block, and bootload code segments of the bitcoin binary. Typically, flash memory is rated between 100,000 - 1,000,000 write/erase cycles (2 - 19 years if cycles happen every 10 min) and that's always writing the same segment over and over. With intelligent disk management to avoid "hot spots," this could be greatly increased. So I would expect even low-grade memory cards to last many years.