It will really depend on who is reading this on whether or not you agree. When a company has a vacancy it tends to go through HR who use a select list of suppliers for all of their recruitment matters. Which is obviously great for them when they need to manage a certain amount of contracts, agreements, constant phone calls and emails from recruiters - but sometimes not so good for a hiring manager looking for a technical person with niche skills!
The agencies on preferred supplier lists for these companies tend to be the large corporate recruiters who have teams of recruiters working on various accounts with no real knowledge of specific technologies that end up working various jobs throughout a week - Fine.
However when it comes to a niche or 'specialist' technology it's not as simple as placing an advert online or spamming out an email to a database of irrelevant candidates! This is where being a specialist recruiter comes into its own.
I have had clients tell me many times that their PSL has had a job open for over a month and nobody is interested! Within a couple of days they have interviewed and offered a perfect candidate which the PSL may never have been aware of - WHY?
Well its certainly not because I am some kind of miracle recruiter who has a magic formula that members of PSL's don’t have. I'm a member of a number of PSL's, however they are only relevant to the technologies I specialize in. By keeping your finger on the pulse and interacting with people in these areas on a daily basis you are much more likely to know who is available at any given time and who might be suitable for new openings! You will create a much more extensive database of candidates who will treat you with respect as they know you have knowledge of the work they perform day in day out - because they will inevitably have to contact you at some point when they are back on the job market.
So I urge any managers who have a requirement and don’t know where to turn when their PSL hasn't supplied the goods - contact the specialist recruiter who sent you an email in the last month introducing themselves to you!