My Smallrig follow focus has been a good investment, but the gear (43T or 43 tooth) is designed for fairly short stills lens focus throw. To focus a stills lens from close to infinity may only take 60-90 degrees of rotation, which the 43T is ideal for.
The problem I have arises when you have the option of setting your stills lenses to a longer 180-270 degree throw or you employ actual cinema lenses.
My Spectrum, Sirui and IRIX lenses are either 270 or 180 degree throw, which when used with the 43T takes two or more full rotations of the focus wheel to go from close to infinity focus and usually requires you take your hand off, interrupting smooth focus to go from even near to relatively near. This means it is sometimes easier to just use the lens as is, which is pointless.
The 65T gear, discovered when I was looking for a rotation handle or similar for the follow focus rig (it has a square hollow in the handle that looked like it might have a use, but no) effectively halves the rotations.
The gear wheel is about twice the size of the original, making the focus rig quite a bit bigger, but the throw is much better and the focus wheel sits out more evenly.
I will hang on to the 43T for the odd stills lens I may adapt, but I doubt I will use it otherwise except for maybe macro work.
ed. another benefit is when the rig is reversed (when on a shoulder rig), the focus control now sits out far enough to be turned with my right hand.