I am not an expert, but in a recent class I attended we discussed the different Tripods and Heads. One of the students had the Giottos MH1302-652 Series II Ball Head, it was very good, even the instructor stated that he uses it (sales pitch maybe), but the good thing about it (as stated) was that if you want to move your framing one degree at a time without loosing the other settings, this device will meet your need. Let me see if I can create a situation to illustrate, assume you are shooting a Pano, you need to maintain everything at the same level meanwhile turning the camera from left to right or up & down, this will allow you do so in the same plain of choice step by step simply by turning one of these knobs as shown.
Whereas, other models if you loosen the part you need to change chances are that you might move it more or even less than you need, hence the need to recompose.
IMO, it is a matter of preference, which one do you feel more comfortable with using. Many times I wished I have the Manfrotto 804RC2 Tripod Head style type of heads. Also, it all depends on the type of photography you want to do eventually the choice would be. As I said I am not an expert, maybe others can shed some more light.
