Using a Micro SD card for data logging, bad idea? Reliable?
We've been maintaining a network of loggers (60+ currently deployed) using SD card connected directly to the SPI pins (see: http://www.mdpi.com/1424-8220/18/2/530 for details) and our experience is that the SD cards are really reliable provided you don't have a brown-out when they are writing, even when we abuse them with hot surface deployments in the tropical sun. And we buy them used, (since the older, smaller Nokia &amp; Sandisk cards have lower sleep currents) but test them well with H2testw.
 However there is one problem that develops over time: the actual SD adapters are not made that well, and tend to have solder flux residue left on the little pads used to hold the contact springs, and these will corrode over time if moisture gets in. I give everything a sonic bath in 90% isopropyl until the parts are squeaky clean, and then always put 2x10gram desiccant packs into the logger housings (with color indicator beads). If you are careful about the cleaning, the contacts last for years, but if you forget, and moisture gets into the housing, then the SD card contact spring solder points are often the first things to corrode.