The HE is plumbed into one of the heater hoses. The hose into the heater will be running at a higher temp. than the outlet, but I don't think this will make much difference. The idea is that warm/warmer/hot water is better than cold/colder/freezing water.
The hose from the washer bottle via the pump is split/extended with the hose going in/out of the HE. As your car heater is designed to operate as soon as possible from a cold start up, the water in the heater hose quickly heats the water in the HE. That's the first part of the science. The now heated water in the HE remains there until needed. Heat soak from this heated water will flow in both directions i.e. back towards the water bottle and onwards towards the washer jets. This helps as the further the HE is from the jets, the greater the heat lose as the water flows in the washer hoses. On mine, once the system is fully warmed, you get bubbles coming out of the jets (this is without using the washers). Once this has happened, warmed water is available even when you just give it a quick squirt. There is a transitional period between water from the heater hoses being hot enough to heat water in the HE and water being heated all the way to the jets. In this scenario, you will need to give a longer squirt to make certain that the heated water in the HE gets all the way out to the jets.
The temperature of the water getting onto the screen is dependent on a number of factors incl. temp. in heater hose, ambient temp. and therefore under bonnet temp. length of hose from HE to jets and heat lose in the system. What I can tell you is it works and if Saab supplied/supplies them for there motors, they must do so for a reason.
Once I have fitted one in the Shogun, the spare will be for sale.
Roger
Roger