I find the oil heater works decent in NY, where it can get pretty cold in the winter. I dress warm for the ramp though not more than jeans and a sweater, occasionally a light jacket.
If you are venturing off base not a bad idea to have warm clothes regardless if you have an unplanned landing!
The other benefit of the oil heater vs. Shroud unit is potential risk of carbon monoxide in the cockpit from a heating unit malfunction.