The classical 6:1 full thickness mirror does take longer to cool than the modern thinner float version but I feel they are far more versatile. They are much more forgiving when it comes to cell design and tend to keep their figure during temperature changes. Barring accident a mirror may last several lifetimes aquiring several different tubes and configurations as technology progresses but thin quartz modern mirrors are perhaps a step forward and they will stand the test of time I think.