I have two Olds 0-99s. They measure 37" with a level bell. They are great small horns providing the third valve slide is cut and optionally also cutting the first valve slide for a bit of push/pull. No adult fingerings needed. Buy them cheap and add a little investment in the slide cutting and ...

Look at the specs in the second post:
Non compensating 4 valves and 1 ROTAX Rotary Valve Weight: 9,0kg - 19,84 lbs

Under 20# doesn't seem too heavy to me...........