I tried to use them, but unsuccessfully for 18 months, looking for computer/internet/packaging lab based jobs, but was not successful. One retired agency owner told me during my rehab job training for WINZ, many of them build up a database of applicants/CV's to try market to employers in particular fields, and thus can be competitive depending on your job skills/specialties.
But three of my young relatively unskilled nieces (early 20's) easily found jobs from agencies at call centres, though included night shift. And many unskilled young people I noticed, got short term manual jobs through agencies.