I used to use these about 20yrs ago and was surprised recently to see they are still available. Just pop on a compatible flash unit, put it on a tripod & away you go.
A cheap wireless flash setup. :D
They do work, but only at very short range, and they are limited in the application – in that the slave sensor needs to point back at the triggering light, so the slave flash pretty much hsa to point at the camera. Save up and go for a radio trigger like an Elinchrom Skyport http://barkerphotographic.ie/el-skyport.htm – not the cheapest, but absolutly reliable!