Yes, Mi A3 has 3.5 mm headphone jack.
Yes. Mi A3 does support fast charging. In fact, the mobile is equipped with Quick Charge 3.0 Qualcomm technology. The mobile comes with a 10W charger and you can additionally use up to 18W fast charger.
Yes, Mi A3 does support face unlock.
Yes. You can record 4K videos with Mi A3.
The Xiaomi Mi A3 will only appeal to people who really value the stock Android experience and software updates, and who want good camera performance, without breaking the bank. For that specific target audience, the Mi A3 is currently the best option there is in the market.
The Mi A3 combines a striking gradient design with decent internals and a clean software interface with the promise of quick updates. The 4030mAh battery easily lasts a day, the Snapdragon 665 chipset ensures there's no lag, and the 3.5mm jack is back.