In that type of a garage a convection heater would use less fuel, be much quieter, cheaper to operate and keep the garage at a constant temp as long as its on where as a salamandor is loud, depending on how high you have it tends to use quite a bit of gas and shuts down when it gets to a certain temp, cools and then starts again.
In a barn good size barn/garage thats poorly insulated a salamandor would be awesome as it gets hot fast, but I love the convection propane heater of the salamandor i used to have.