I don't think they work well on smaller tractors compared to larger ag tractors. Had one on my JD 5300 when I bought it. It never seemed to send much heat/air back to the operator. On our older ag tractors, you could definitely feel some heat when the engine was warm and feel the air blown back on the operator. I believe the smaller engines just don't produce enough heat and the radiator fan doesn't push enough air to be effective. 3720 is even smaller than 5300. They do however, help keep the wind off of the operator.
Most of the units are now made of reinforced, flexible plastic rather than canvas but otherwise function and fit the same.