I'm not aware of this kind of product, only diagnostic tools. If you keep an eye on your instant fuel economy and you see a sudden reduction that could indicate diesel is being used to actively regenerate the DPF. Other signs to look out for are the cooling fans running at a higher capacity than normal, the stop-start function deactivating or the engine note changing. You could also try putting your window down when you are driving to see if there is a hot, acrid smell from the exhaust.