Amazon are pushing their Amazon Music service (think Spotify) with this great offer. Get a one month subscription to Music Unlimited plus a 3rd (ie latest) gen Echo Dot for £10.98. The price is even less for Amazon Prime members at £8.98.
The Echo Dot normally retails for £34.99 so you're saving £34 even without the month of Music Unlimited. Of course you can cancel the Music Unlimited subscription when the month is up, if you want.