It really seems to depend on the FA. I've had mine since February, and am about 50/50 on being asked to turn it off. If they comment or question about it when I board and bring it out, I ask if they mind me keeping it on. Otherwise, I just keep it out. Most FAs who know what it is don't mind it.
I just put it to standby and close the cover if requested to turn it off. The only electrical impulses are when the page is turned. If it's on standby (screen saver up), nothing is being emitted.