SwiftBackup can be installed on as many devices as you want - there is no limit, BUT you are required to purchase a licence for each computer you wish to backup.
SwiftBackup can be installed on any external or network drive. There are 2 methods for doing this.
Both methods will put SwiftBackup into setup mode which will prompt for a target folder in which to install the software.
It is highly recommended that SwiftBackup is installed on the root folder of the selected drive.
Once the installation folder has been selected SwiftBackup will be copied into a subfolder and an autorun.inf file will be created. If it is an external device such as a flash drive AND the installation targeted the root (top-level) folder then the next time the the device is inserted you will be prompted to run SwiftBackup (only if autorun is not disabled).