As a fire performer who has a collection of ropedarts i find this all interesting. the description of the weapon is correct apart for the fact that it takes 2 hands to wield, i use my left hand to control the length of the free rope and my right hand to direct the dart. other body parts are used to redirect the dart, speed it up, and chose the direction of fire.
As for the range,my ropedarts are all 13-14 foot long and I often both step forward and reach in the direction of fire increasing my range. i would call 20' fair for game statistics but would refer to the dart as a reach weapon unless it is released to throw further as has been mentioned above.
I am playing a human monk who uses a ropedart as a range weapon.
see this video for a ropedart in action.
https://www.youtube.com/watch?v=fxl0cRrCQoc
