I concur with the above info as it was accurate as of this time last year when I rented a car and toured Edinburgh and the Grampian Highlands. Roads are generally good, but I might suggest considering taking the offered damage insurance, as in the backcountry some of the roads are narrow and not in great condition. I was pushed out of my lane by an oncoming truck and hit a pothole on the yellow outside lane line and tore up two tires and one wheel, requiring a several hour delay in my travel plans while the rental company got things fixed (actually exchanged out the car). When I got home I found a bill for more than $800US in damages assessed to my credit card. Tough to fight transatlantic charges like that, even with my credit card company fighting he battle (they offer free extended insurance coverage on rental cars, but there are some restrictions on international rentals).

Better safe than sorry.