i dont run a heater in my puma, which is my only car, and although it has a heated screen it can still be a pain in the arse. if its cold the car steams up without fail. i have to keep a window cracked and thrash the heated screen constantly. ive had cars without heaters before and its always a bit of a pain but managable.

the overheating issue is one to consider though. if your car runs hot then id probably not bother as itll not help things. its not just the fact you have a 2nd heat exchanger but the added volume of coolant helps in its own right.

all depends on how hardcore you want to go i suppose.