I've always used armor-all on the dash and other interior vinyl. Looks good and seems like it protects fairly well.
Not a fan of any Armor All product. They use silicone as well as other low end ingredients. Though it can look nice it has the downside of build up and nothing cuts silicone build up except manual removal. Another note. Your dash should never be shiny. The last thing you want is more glare inside of your car. Shiny looks fancy but it is rough on the eyes, even at night.
I avoid Rain-X for the same reason. Rain-X is silicone in an alcohol carrier. Works great at first. Then comes the streaking and chattering wipers. Weekly reapplication is the only cure. The only way to remove it from the glass is by polishing.
Interior plastics are served fine by the external paint sealant if it is a wipe on walk away.
If you want my advice for a dedicated interior vinyl and trim sealant try. It is matte and very effective. Autogeek sent me a sample last year and I was impressed.
http://www.autogeek.net/gtechniq-c6-matte-dash.htmlMy all time favorite brand just went through a complete re-formulation and I am not happy with the results thus far. Arrrrgghh!
In the end use whatever brand you are happy with, as these are only recommendations per what I have learned over the years.
In case you are wondering, yes. I used to use ArmorAll products. For years. Now I know that there are better products for my cash and car.