Sonicare ProResults heads come in two sizes - standard and mini.
Standard is like a regular manual toothbrush. Mini is about one third smaller.
I find the standard heads too big to properly clean my back teeth, so use the mini, while my wife feels that the mini is too small to be effective and prefers the standard.
So it's horses for courses, and I would recommend buying one of each head to find out which works best for you before buying a multipack.
In both versions the heads, and the Sonicare system overall, are excellent.
Each head lasts around three months.
Five stars.