Before retiring I was an over the road trucker for over 20 years. After I found out this Dist-O-Map was available I never left home without it. This and my regular Rand McNally map have been traveling companions for many years.
True you can figure out distance from the regular Rand McNally map, but it takes some effort and crossing lines to do it. This Dist-O-Map is a snap to figure out. Just turn the round outer disk to where the hole corresponds to the city you are at and the other holes with the miles line up to other city's. It's easy to use, made of sturdy glazed cardboard that should last for years plus you never have to replace it until it wears out.
It comes in a book form, each page is a different section of the country. Certain city's overlap to the next page allowing you to keep going. There is one page with the whole United States and certain key major city's on it. No this is not a must have for traveling, but if you are anything like me and like a fast easy way to know how much further I have to go this is it. Not very useful for short local trips but for longer trips I found it to be quite helpful.
And NO it is not incredibly flimsy as one negative reviewer said. I have had a couple of these over the years but I used them regularly. I would say each lasted approximately 4 years with a lot of use.
I have had mine for quite a few years now. Since retiring I don't use it nearly as much as I did but nevertheless it still goes with me when I'm going on a longer trip.