What are some alternatives?
When comparing CellSend and Dukto R6, you can also consider the following products
Pushbullet - Pushbullet - Your devices working better together
FilePizza - Open source application used to transfer file via WebRTC and WebTorrent.
Pushover - Real-time notifications on your Android, iPhone, iPad, and Desktop
Send Anywhere - Send whatever you want, wherever you want
AirMore - AirMore is a cross-platform toolset that can help you manage any Android device wirelessly.
SHAREit - SHAREit allows you to transfer files and data from your phone to another device without having to rely on WiFi or a data plan.