Cluster and express are not the same thing, express are single individual (not clusters) eyelashes placed onto the lashes WITHOUT isolating they last 2 weeks and then must be removed otherwise your clients lashes can be damaged, cluster lashes are 3/4 lashes on a bulb some times called party or individual lashes or weekend lashes they are also sold as individual lashes despite not being individual these last a few days and are placed on the skin, strip lashes are on strips last a night. Semi permanent eyelash extensions are isolated and each natural lash has 1 extension (sometimes 2 with expertise) attached to it they are fitted appprox 0.5mm from the lash line so do not touch the skin last up to 2 months with no maintenance or can be Infilled 2-3 weekly and last until maintenance stops
Hope this clears up confusion with what lashes are what.