Their speciality matters, a PR manager with Crowd Involvement helps your team perform slightly better at home, and one with National Appeal helps your team on road games. The effect doesn't matter for the level of PR-Manager, so if you just buy a basic manager with speciality you get a small boost in performance for a small price.
As for attendance boost, I haven't heard of anyone showing that the increased income from extra attendance is higher than the weekly pay of the PR-Manager, so I wouldn't buy one to get better income from attendance.