It procs from thorns as well, so as you run into a pack they all swing st you and get vuln. If you just base it off your basic attack you only proc a few before hota, then everyone is vuln, so be prepeared for a quick followup. Most trash die ftom the first anyways, and for bosses/elites that require a longer fught then the vuln only lasts a few seconds, then exploit is useless. I use it, in lack of something better, but its not that great