I have travelled through Heathrow, London at the height of the terrorist scares with a gun-shaped spotmeter in my carry-on bag and never once had it checked. I thought it would cause a problem at the time, but it didn't.
Over the years I've travelled regularly with my spotmeters, they can tell exactly what they are on the scans, its more unusual objects they question.
I had security ask to see my Wista at Izmir once, and that was more out of interest to see the camera, as they'd never seen anything like it before, and in Chile at Santiago Airport they couldn't recognise my 6x17 camera, the attached cable release didn't help.