Hi Tar, how long the diamond rods last depends on how you use them. If you use too much pressure you can literally strip them out in a day. If you keep the pressure light they will last for years and years. I have a set that is 4 years old and they have probably reprofiled 80-100 knives and they are still going strong. No, they are not quite as aggressive as a new set but they are still very capable and should be good for several more years of service.
As far as cleaning them, I just rinse them with soap and water. They do not require the "scrubbing" that the the ceramic rods need.