I tend to always use the ISO image when installing a new Delphi. With Sydney, Embarcadero went to a full Gettit installer setup for improved and consistent installation experience.
One issue many have found after installing from the ISO is that Gettit no longer works after competing the IDE install.
To resolve, Gettit must be placed back into online mode with a simple command line.
GetItCmd.exe -c=useonline