Most of IoT products works with a simcard and GSM module. So if you want to use OTA function fo furtur upgrades on your devices, you have to use an OTA server witch support smal packet requests due the gsm limitations make the device to download a large file in several smal parts.

Espressif ESP32 and ESP8266 modules are very powerful to develop any type of IoT product such as wireless sensors or actuators as cheaply as possible. It's very useful to implement some HTML pages in your IoT device to let users change the settings of the device or do some operations with a cell phone or desktop computer.

It is popular to show a progress bar to the user while a lengthy operation is in progress. Formare OTA upgrade is one of the lengthy operations. It may take from 5 seconds up to one minute to complete. It can make the user bored and the user concludes that the device is stopped working and do a hard reset.