Off center ball head or center ball head

[Hazel]

Hi,
I would like to have some recommendations on a tripod head. I got a Gitzo tripod with low profile tripod head. I have come to limitations on the vertical shots since it's not possible to bend downwards. So I was considering a Ball head or maybe a Off centre Ball head but was wondering what the difference between those 2 are.
Hopefully someone can give me some advice.
Thanks,
Hazel

 

[usayit]

limitations on the vertical shots since it's not possible to bend downwards.

I don't quite understand. Vertical shots as in turn the camera on its side like this

or vertical shots as in pointing the camera towards the ground? like this

 

[Hazel]

Hi,
Re first pic, yes that is what i mean with vertical shots. But what if I want to bend the camera downwards or upwards with an angle of 30 degrees. This is not possible with my gitzo low profile tripod head. So that's why I'am considering a ball head. What I would like to know is what the difference between an off center and a center ball head is. Is the one better/more flexible/easier to use than the other?