Well, overall I think that large bike mount phone case is pretty good even though I got to near immediately realise why I was quite reticent about having one.
Tuesday night, arriving in Carlisle, unbeknown to me there is a big wide metal plate at the end of the Rickerby park cycle/footbridge.
Whilst it is lethal when wet, it was the Sustrans right turn sign placed exactly at the plate braking point that helped bring me down. Luckily my phone and the mount survived, rotating 90 degrees on impact.