In this case, as the house is in Limerick and you are in Dublin, I think you should be looking at a letting/management agency. Letting agents only vet the clients and set up direct debits for you whereas a management agency will attend to call outs etc. if anything goes wrong. You can hardly drop everything and rush down to Limerick in the event of urgent repairs etc.
In general I don't use a letting agency, but I am located quite close to investment properties. All agencies will negotiate on fees IMO.