I've used their service on a trial basis - you can set up a free trial with one euro credit - only difference is the local number they give you is not dedicated to you as it would be for the proper service. They will give you a dublin number but if anyone rings you on this number they have to enter a 5 digit code dedicated to you to get through to you.
Works very well - you dont even need a real voip phone to use the service as you can download a free "softphone" and use a headset. However, quality will be better using a hard phone.
Therefore, if you want to, you can abandon your landline and get a local dublin number for Eur10 a month (basic service) that includes 300 worldwide landline minutes per month. No line rental.