The slimline motor (25mm) can be used with the Titan extruder range but it is right on the edge of the torque output required and therefore requires substantial calibration for reliable printing and the maximum print speed would not be as high as it would be the compact but powerful motor.
The compact but powerful motor (40mm) is the recommended motor for the Titan Extruder range it has the ideal amount of torque for reliable printing with the Titan Extruder which is why it is the additional motor option.
The compact but powerful motor can be purchased via the following link: https://e3d-online.com/products/motors
Documentation on our motor range dealing technical specifications can be found via the following link:
https://e3d-online.zendesk.com/hc/en-us/sections/360004174038-Motors