I would put it to you this way then, consider your propane bill from last year and compare that to how many times you used propane when the outside temp was above 45 degrees, if its very low than it might not be worth the extra investment. But if its high, meaning you used propane a lot even when it was above 45 degrees outside then yes you should see a return in investment quickly. I'm not trying to take anything away from the contractors you are talking with I am sure they are great people. Is just that sometimes people will try to sell folks things they don't actually 'need'. The reason I say that is because everyone's living style is different, some like it cold some like it hot lol.
For what it's worth, heat pumps are used vastly here in central florida because believe it or not, it can get a little chilly for a week or two lol. But a resistive type electric strip heater can tax the electric bill considerably. The biggest motivator for heat pumps though are the fact that they are the most efficient in heating and cooling due mostly to their coil capacity and heat transfer capability.