I have numerous backpacks and laptop bags at home, and problems with my shoulders now mean it's wheels for me.
It's quite a manly 18" one, if you know what I mean... Vanity case it isn't.
Anyway, back to the original topic there are actually two positives:
1. There was no queue at all at security
2. One of BAA's staff members actually applied some thought
I don't think it was completely "invisible", more that there was no restriction on seeing the contents of the laptop or iPad.