Many thanks for your explanations. When I tested the A7/A7r in a shop, I found the behavior of the magnifier very annoying, since my eyesight isn't very good and I'm rather slow at MF. I assumed that how long the magnifier stays on would be configurable in the customization menus, but may be not ? May be that I have been spoiled by the Olympus interface ?
The magnifier does stay on for the time you set in the menu. It can be 2 sec, 5 sec, or forever. I have mine set for 5 secs as I have rubbish eyesight and it works perfectly for me.