To be honest, I haven't checked the content of the onion link so I don't know what their position is (or if they even communicate it), I will assume that you're describing their it accurately.
> they believe that there should be no use tax on public transport and that people who don't use it should still be responsible for financing it
I don't know for Manchester specifically but any public transport I'm familiar with is payed in huge part with tax money, so people who don't use public transports are already paying for it. But not the 100%, instead it's balanced with the use tax. So, is that the contention point, that it should be paid only by tax money? I don't understand what benefits that would bring. With this system, people using public transports the most (thus get the most value) would pay the less (if averaged per trip), how do you balance such a system?
Concerning their action, what's the idea behind sharing their exploit other than simplifying the work of free-rider? That it is too expensive to design a use-tax system that works, thus make the 100% government funded solution more attractive?