There is quite a difference in the grip of the CP88 and CP99. The CP88 is fairly wide (esp with wood grips as shown), the CP99 is more slender/comfortable for small hands. As mentioned by Gareth, the CP99 comes with an alternative back strap. The hammer on the CP88 can be accessed for SA shoots, the CP99 can be cocked using the rear slide for SA shots. The CP88 tends to be favoured possible because of ease of SA shots and the simple lever method of piercing the CO2 (CP99 uses rotary action to pierce bulb). Also longer barrel and comp sight options for the CP88.