We are a DTUK dealer, and have been for a couple of years or more now. They are warranty safe, and you still get the protection of the ECU, as it piggybacks. You have certain adjustability as well, but we know what settings these vehicle run on best, so usually most people leave them, how we set them.
Happy to demo if you're local. On a 140, it will take it to around 180BHP - They totally transform the vehicle whilst retaining your warranty.