The only thing I would say with the back to black stuff is you won't be able to see out of the windscreen when the sun is reflecting off if your dash and causing serious glare. Ask me how I know lol
Try the autoglym trim restorer gel stuff (can't remember the right name) did mine and it last for ages and cause you rub it on with a cloth it doesn't get everywhere like the back to black spray stuff
Just for people who may come across this post in future times, I brought some "Back to Black" and applied it to my dashboard at the weekend and it made a massive difference. It covered most of the stains and the marks on the dashboard and put a shine brining it back to an almost new look. If you have a dashboard that has discolored, then certainly give this a go.