What are some alternatives?
When comparing SHAREit and AirDroid, you can also consider the following products
Send Anywhere - Send whatever you want, wherever you want
Pushbullet - Pushbullet - Your devices working better together
FilePizza - Open source application used to transfer file via WebRTC and WebTorrent.
Mobizen - Use your Android from a web browser or desktop.
Dukto R6 - Dukto is an easy file transfer tool designed for LAN use.
AirMore - AirMore is a cross-platform toolset that can help you manage any Android device wirelessly.