Hi Otto,
I think there's definitely a range of people re. how they will react, and it might depend how defensive the person is. There are a few people who I, if not criticise, then suggest alternatives to their perspectives in my work. I dont aim to outright criticise them and their work. One of these people has taken it all very well and said my work is very interesting, the other went on the major defensive and tore my work apart (mostly with completely wrong and unjustified criticisms). Think the problem with the latter was that my supervisor said I should go and present my work at the institute she runs, so she may have felt extra defensive there. I would recommend not doing it face to face, and making it out that you are interested in their comments rather than you want to blatantly criticise them!! Australia seems like a nice long way away...