The £2000 price ticket is in the same ballpark as the Multiwash machine. You can get a good deal from your friendly neighbourhood Truvox dealer
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They are amazingly productive units due to all the weight being on the brushes.
The Osmo machine is a slightly different spec from other machines out there in that it uses the tank normally found on the multiwash models with a sprayer built in but uses it to top up the gravity fed solution tank of the standard models for increased capacity. This is a great idea considering that on decking a fair bit of cleaning solution will be lost between the deck boards.
When we use our machine for restoration cleans we would wet the boards first with water. Apply the chosen cleaner with a watering can then scrub with the machine. When we do this we take off the rear waste tank and drop its lid down to act as a splash guard. This way it drops the solution back onto the deck for added contact time. We then vac off and low pressure rinse, often with a garden hose, so as not to open up the fibres of the wood. Yes this means additional kit required for the task but we find this most productive as the waste tank doesnt hold a huge amount of water and requires frequent emptying.
When working on interior flooring we would use the dispenser system and recovery tray so as not to overwet the wood. It leaves the floor really dry (with soft black brushes) and removes a remarkable amount of soil with such low moisture.