Is it necessary to have a micro SD card inserted into the Crystalsky?   

No...I use it for additional storage, but they are not required.

Tviscomi Posted at 2018-1-6 18:02
No...I use it for additional storage, but they are not required.

Thank you.

Equipped with dual Micro SD Card slots, the CrystalSky monitor’s storage can be extended, or footage recorded on a Micro SD Card can be played back directly on the monitor. It can also be used for footage backups. Using editors built in DJI GO, high-quality edits can be made quickly and instantly shared to social media.
It is also fine without SD card.

Thank you Tviscomi and Mindy.