garage heating

[Aurora40]

Anyone have any experience with heaters like this?

http://www.mrheater.com/ProductFamily.aspx?catid=57

I like that it doesn't need venting installed, and the wiring is simple as it's just a 3-prong plug.

I wouldn't use it continually to keep the garage warm, rather on-demand. We have natural gas, so it would be nice to use that to heat the garage. Any thoughts on the brand, that style of heater, etc?

I have a fairly small 2-car garage, probably about 20x22x9'.