For management something like 5% plus VAT at 23% is a good benchmark. It depends a lot on the type of property and rent though. For an agent there is not much difference in the work between a €1,000 and a €2,000 property. If you are a top-rate taxpayer the cost is effectively halved.
The main pros are that they have ongoing relationships with retailers and tradesmen who will take their calls as they get repeat business. Cons are that agents are probably less picky than you will be yourself at the start. They just want a quick letting and if things really go south the landlord has to step in anyway.