How long the cups last?

You can safely use your Lunette Cup for several years — there's no need to replace it annually.

If you notice any signs of damage (e.g. cuts or any deterioration) on your cup, or if the cup has discolored and collected surface debris or biofilm you should get a new one.
But please note that strong discoloring or built-up surface dirt on the cup can make the silicone material more susceptible to cuts or harden the surface. 
PS. You can prevent discoloring by always rinsing your cup with cold water before cleaning it using the Lunette Feelbetter Cup Cleanser! :)