Not all microSD cards are created equal
there are several types, brands and capacities to choose from.
Micro SD cards come in three capacity classes: SD, SDHC and SDXC.
Standard SD cards cap out at 2GB, so not really a worthwhile choice for audio. SDHC cards go from 2GB to 32GB. Not a bad choice for audio use. If you need to record lots of channels, at high sample rates, or simply want a card that has so much capacity you can just leave it recording for hours at a time, the SDXC cards would make sense. They are available upwards of 32GB, even as large as 400GB. 1 and 2 TerraByte XC cards are planned for release in the near future.
Besides capacity, the next spec to pay attention when choosing SD media is speed.
The Aurora(n) is capable of writing up to 18/MB per second, if you were recording 32 channels at 192k. So we want media that gets close to, or exceeds, this mark.
There are several speed classes available. The class we have tested thoroughly and recommend as a good target is UHS3. UHS stands for Ultra High Speed, and UHS3 can operate at 30MB/S. UHS1 can be fine as well, if you do not need high channel counts at high sample rates. UHS1 can do 10MB/Sec
In general, we recommend sticking with brands known for high quality media, such as Samsung, SanDisk, Kingston, etc.
To review, a good place to start would be a 32GB, UHS3 microSD card, such as the SanDisk Extreme or Samsung Evo.