Optional M.2 PCIe SSD slot for upcoming AeroBook Pro 15.6 -

What are the characteristics of the optional M.2 PCIe SSD slot of the upcoming AeroBook Pro 15.6?
Which will be the best type/brand of SSD for the optional slot?
I have read about M.2 SATA 3 NGFF and MVMe. What is the difference.
I have booked the AeroBook Pro 15.6 and will want to buy an optional SSD in advance.