I've ridden a couple horses of both the breeds you're talking about and I've enjoyed my time on both of them.
I leased an Oldenburg for quite a while and he was a joy to ride. Occasionally a little hot, but overall very willing and a real "trier". The Irish horses I've ridden have all been pretty intelligent and also very, very willing as well. They all really seemed to want to do things right, but they're also more apt to be a little more like, "Uh, are you sure we're going to do THAT?" I rode in a clinic once with Eric Horgan and a friend of mine was on an Irish horse and the horse kept getting put off and stopping, but it was always a pretty honest thing where he realized the rider wasn't sure what she wanted. Eric Horgan just said, "You know, you can always tell when an Irish horse is going to stop far sooner than you can tell for any other breed I've worked with."
Overall, I've enjoyed working with both breeds, so I think a cross of them would be pretty awesome to work with. All horses are individuals though, so just keep that in mind when you go look at this horse in particular.