I don't quite get what benefit there would be from TDE on Express. TDE only is useful for the data "at rest": if you have physicial access to the server and you're SA on the server (i.e. the default setting in Express), you have full access to everything in the database. Sure you're can't steal a backup for the database, but then again - you can simply go in and execute "select * from mytable".

I don't deny that it could be useful to ensure that your backup media is encrypted (unless you don't keep track of your keys in a separate place, in case you're essentially scr***d, but still - I think we're overselling its usefulness.