It didn't benefit me as i got routed to London from the north west when routed via their manchester peering offered lower latency to several destinations and make little sense IMO being routed via London everything should not revolve around that place
I still have a line in 020 7/SE1 which is routed via Manchester... All the others go where there supposed to (London)
In my case it was their link at my exchange that had been set up this way and told me it was unlikely to be changed, and this was a recent exchange presence for zen, you would think for those located nearest to their manchester Peering points would be routed to that, and those in the south of the country via london