If its a single operator sysem it will have one heat exchanger. If its a twin operator one it will have 2 heat exchangers. The twin operator systems are more expensive. Heat exchangers and the thermo control temperature valve are expensive so add to the price.
PF don't mention if the price on their website is for a 2 man system or not. They call it an Isothermal 2 diesel fired heater. It could be that the 2 donates that its a 9kw unit as opposed to a 5.2kw unit they used to do. You need to ask the question. And don't think the illustration showing 99C is what the heaters will heat the water to. They won't.
If you look at Streamline's site you will see they actually list 3 'upright' heaters.
The first is a single operator 5.2kw, which will be the cheapest, a single operator 9kw and a third twin operator 9kw unit which will be the most expensive. Heatwave use the model Thermo 1 for the 5.2kw and Thermo 2 for the 9kw units in either single or twin variants. So there model number is boiler related.
http://www.streamline.systems/products/186-heatwave-thermo-2-horizontal-double-operatorCleaning spot have listed the Thermo1 at £2799, the Thermo2S (single operator) at £3699 and the Thermo2D (double/twin operator) at £4399 all + VAT. To confuse you, they have used the illustration of the Thermo 2D for all three units. So actually the Thermo 1 and Thermo2S will only have 1 temperature controller on the side and only 1 heat exchanger.