I have to admit I have never seen one that large. But I am thinking that vibrators that large would leave a large void when withdrawn that would tend to fill with free water and fine grout rather than well mixed, consolidated concrete. It has always been my understanding that you choose the smallest vibratory head that will be adequate to keep up with placement of the concrete. The largest heads I have ever heard of are 3 1/2 inches, those appear to be much larger.

Concrete Construction Article PDF_ Choosing a Concrete Vibrator.pdf

As always I am open to being further educated.