Be careful, the Tello can overheat even during the firmware upgrade process!! I did a test flight after the update, and the Tello shut off MID-AIR (!!!!!) because of overheating!!! Fell down the floor from 1m height...
Yesterday I noticed that the plastic cover has a visible hairline cracking near the USB port, and also a lighter one near the Power button. The hairline crackings are following the same path both sides. Maybe the plastic has a tension there, and we'll see cracks similar to the P3 series? :-O...