You can view a summary of your transfer — including recipients, files, expiry date, and message — while it's uploading or after it completes.
While the transfer is in progress
After clicking Transfer, click on the line that says 'Sending x files to x persons' to open the Transfer Progress Panel. This shows all the details of what you're sending and who you're sending it to.
After the transfer completes
Click the 'See what's inside' button to view a full summary of the completed transfer, including the files sent, their individual sizes, the total transfer size, recipients, expiry date, and message.