No. Vivo NEX does not have the front camera led flash but it does have the display screen flash, similar to Apple iPhone retina flash.
Yes, You can play 4K videos on Vivo NEX.
Yes, Vivo NEX does have the face unlock support.
It takes about 30 minutes to charge Vivo NEX from 0% to 50%. Vivo NEX comes with 22.5W output charger.
The Vivo Nex S is a unique smartphone. It looks great, it’s built beautifully, has the best processor you can currently find in a phone and a huge, truly edge-to-edge display.
The Vivo Nex brings some truly cutting-edge technology to the table but does so with an all-too-common mix of familiar failings. Even though we don't think it's the phone you (or we) really wanted it to be, it's still one of the most exciting phones we've seen in a long time.