Four questions, worth asking of any firm including this one.
Where do your placements come from? What share arrived by application versus by direct approach. This sorts the models faster than any category label: if most placements come from people who applied,
that is a staffing model whatever the firm calls itself.
Who runs this search day to day, and are their names in the agreement? Firms separate business development from delivery as they scale. That is a normal structure, but you should know which people you are getting.
What percentage of our target list is off-limits because of your existing client relationships? Every client a firm serves removes companies from your addressable market. Ask for the number.
What prior relationship do you have with the candidates you will present? A firm meeting candidates for the first time compensates with references and interview rounds. That is a legitimate method, and a different one from having known someone for years.