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You're right. The Pro's are a newer version.
Usually Bike-24 is the cheapest but Wiggle and Chainreaction both have them on sale at the moment.
It might be worth looking at the IRC tyres that @Mu_Mu posted about earlier, I've only heard good things about them, @cycleclinic sells them.
https://thecycleclinic.co.uk/collections/road-tyres/products/2017-irc-formula-pro-rbcc-tubeless-road-tyres
Best place to get a Pro One?
I take it the One is a shitter version of the Pro One.