Doh! The Sony flash hotshoe has a different position for the locking pin

I kept thinking that the Sony hotshoe was dodgy because the flash foot of other brand flash seemed not to fit entirely in. It's actually by design - the locking pin to centre pin distances are different in Sony vs universal shoe design. Make sure the locking pin locks and you're good to go. The other brand flash needs to be on Manual and the Sony body needs to be on Manual Exposure because there are no secondary electronic contacts except the centre pin which triggers the flash. In fact, my Sony a7 does not even know the flash is there as it does not limit the shutter to the maximum flash sync speed. I found faster than 1/160th second, I could see a curtain shadow - the camera body itself does not limit the speed, you just have to remember it.