An interesting idea. I don't believe in more power or range - RPi is a low power device - but if this adapter breaks the limitation of the number of connected devices the built-in adapter seems to have, this could be an expensive workaround.
I don't have this adapter nor have experimented much with other wireless adapters for RPi. The product page https://www.alfa.com.tw/service_1_detail/13.htm doesn't mention the max. number of connected devices. Following its chip found that somebody has compiled the driver for the RPi as a Linux module: https://layereight.de/raspberry-pi/2016/08/25/raspbian-rtl8812au.html. Once that is done, assuming the driver supports "hot spot" mode, you still need to reconfigure MoodleBox to switch the wireless adapters. So, not something one could just jot down without trying.