I have factory navi in my x5 , so far i like it but i am used to my avic-d3 navi and interface is friendly. As i am writing this, there is a lot of retrofits navi for x5, that looks the same to each other but different in software. I was told and read myself, some known bugs out there exist. My suggestion would be to wait and research as everything will be getting fixed.
Type here in search bar navi retrofit, there will be several. Also on youtube as well there is a lot of videos about navi for e53 with demonstration