Cermet is so hard that it is said that you can take a file to it and you won't mar it. Heat dissipation is practically instantaneous, and weight is even less than SIC, especially if you buy titanium frames. Service life of the guide will be longer than you can expect to be on earth. Reportedly impossible to mar, even with a file. Take out a second mortgage on your house to buy a set.
Nothing is indestructible.
Until I hear otherwise, I assume that the rings can be shattered. But then, if you break a ring by slamming your rod tip in the car door, you probably won't be fishing with that rod for awhile anyway. The best way I can convey the differences in the performance of Hardloy, SIC and Gold Cermet is to repeat a story told to me by another custom rod builder. The local Fuji rep came in to do a short seminar for everyone. Hardloy vs. SIC vs. Gold Cermet.