Try and avoid products that give a 'shiny'/gloss effect because that just makes the dashboard look horrible and the majority of these products contain silicone that can make the windscreen look a right mess if that particular silicone containing product is accidently sprayed onto the glass. Have you ever saw that 'rainbow' effect you see on a lot of police car windscreens? Thats completely down to the silicone.
If possible, try and use a semi matt product that brings out the natural colour and keep its looking 'natural' if you know what I mean.
Only use 'shiny' dashboard products if you own a london taxi cab.