A No-Glow flash is going to produce a black and white picture and will NOT be visible in the dark.It produces no visible light unless you are very close to the camera and will be nearly invisible in the dark. You can confirm whether the modem is in CLTS mode by sending AT CLTS?
The fact that it uses a character after the AT implies it is a common (as opposed to proprietary) command, and should be available on most if not all cell modules.
An infrared flash is going to produce a black and white picture and will be visible in the dark.
It produces a dull red glow that is not bright enough to catch your attention in the dark but if you looked right at it, it would be visible.
The memory expansion slot is shared with the second SIM slot so you can't get both dual-SIM and micro SD at the same time, though.
In terms of connectivity the Samsung Galaxy offers 4G LTE, dual-band Wi-Fi, Bluetooth 4.1, GPS with Glonass and Beidou support, as well as NFC.