If you have a TomTom that supports this TMC Cable (Easy to check using their site)
I highly recommend that you spend the money for one. Easy to use, just plug in to the USB, the first time your TomTom will accept the device and if required you can have a quick demo of how it works on the screen. The TMC then shows you a bar with your current position and if your journey involves traveling into any Road Works, Accidents, Incidents it will show you how far they are and also how long the delay may be. If you have IQ routes it may also consider another route avoiding the issue altogether. On the whole and on the journeys I have done so far it has been worth the money in saved "time" alone. Please Note - The devise is only has good as the data being transmitted.