Good agents are pretty rare, and can be very useful,if not essential. In the industry I work in (engineering) there are a few guys who have a good reputation, are trusted by clients and treat candidates well. The majority are hopeless, but once you find your feet, it’s easy to work out which are the ones to avoid, as they will usually give themselves away within the first phone call.
I don’t have much time for the commonly held view that they are all leaches…IME it’s not true. There are good ones and bad ones, and if you treat them all as ars******, you will end up dealing with the bad ones, and it becomes a self fullfilling prophecy.
IME decent clients eventually find decent agents, and the same goes for candidates.
In the OP you ask if there any benefits of using an agent, and in many cases, its a moot point…the client won’t deal with you directly as they hired an agent to find someone for the role. Aside from that, a decent agent can negotiate hard for you, give you a market overview one outline options, filter out the bad clients, give you a constant stream of work and manage the client if you want to move on.
You say you know someone, I’d go and talk to him. Also talk to other people in your industry to get a feel for what’s about and who are the decent agents. Agents are a classic example of something where you want a small number of the good ones, not a big number of the average ones.