After physical experiments with a real life user. The most comfortable handle designs were: Model 1 & Model 4. 

These models felt the most secure and for the user with the larger hand left enough room for all fingers to wrap around form comfortably. Not too large for the smaller hands. The closed curve on the same side as the majority fingers felt most secure. 

This iteration of models for completed to establish part splits and CAD modelling further.

Simplifying geometry of the form and still leaving the previously functional ergonomic curves and proportions.