The propensity for USB sticks to go missing, get picked up by somebody else and so on means that data on it is not safe - unless you can password protect and encrypt the data.
And that's where this comes in. It works well on my Macbook Pro - plug it in, click the application icon (after a quick scan of the user manual) and then type in a password. It forces you to choose one that is over 6 characters long and has upper case, lower case, numbers and special characters in it.
Each time you plug it in, you are required to enter the password to unlock. Then when you are done, you click 'lock' and eject and away you go safe in the knowledge that should you lose the stick or should someone else get hold of it, they can't access the data easily.
Depending how 'top secret' the data needs to be, the downside is that after 6 wrong attempts at the password it will wipe the stick clean. So whatever you do, do NOT forget the password!
I transferred a file of photographs (213MB) and it took just about 30 seconds to transfer, so not too bad from a time perspective.
I've only given it 3 stars because you can buy this - Integral Courier 197 4GB USB 2.0 Flash Drive with 256-Bit Hardware Encryption
for considerably less and it has lots of positive reviews too.
I can't think of anything that would make this work the additional £12.
Hope that helps