I use a hot water 600 litre Thermopure system out of a Trafic van and it is possible to use both hot and cold. Having had the benefit of using hot water, personally I would not go back to using cold, even though a hot system costs more to purchase and to run.
In the winter it is a godsend, but in the summer it is good too. Gets the windows clean without having to scrub quite so vigourously.
If you are on a very tight budget then don't get hot, just get cold. But if you can afford it it is worth the extra money.