The letting agent was useful for setting up appointments for viewing properties, instead of having to do all of the legwork ourselves. However, you're limited to the properties that are listed with that particular property agency. They won't deal with properties listed with other agencies.
In our case, we visited the agency that had the most listings in our desired neighborhood and went from there.
90% of the time, the listings that were on rightmove.com had long since been taken.