To those who ask why…
I don't know yet!
By next spring I might know. A winter of grit, muck and filth will either wreck the belt and pulleys or have little impact. If it's the latter then I will be happy and will probably convert my other singlespeed. If it's the former I'll go back to chains and write the project off as an interesting but expensive experiment.
Weight wise the pulleys are probably about the same or slightly ligher than an aluminium chainring and a steel sprocket. The belt is much ligher than a chain.
According to the manufacturer the belts don't stretch at all. I imagine that when it's worn out the belt may start to 'ratchet' or jump teeth. Should certainly never snap unless it's mistreated.
It is noticably quieter than a chain and I do really like not having grease on my calves, clothes, car and carpets.
Changing tyres/tubes is no different to on any other singlespeed with horizontal dropouts and a chain tug.