I think the point a few of us are making here is that we want a bag to look like it contains nothing special, and nothing of value to attract malevolent people.
The problem with Ona and Billingham, unless they're old and worn, is that they simply look like what they are - expensive pieces of luggage. This in itself signals money spent. The added problem with such bags is that they may look like they contain laptops - which a lot of them are actually designed to do.
Photographers spend a lot of time wandering about alone in places where there is nobody to come to their aid if they are robbed. This can happen even in urban parks and green spaces, or in the street even. Their bags can easily contain $2,000 of equipment.
The point of all these unidentifiable bags is to give out the message "this contains books, sandwiches and a rolled up raincoat" or something like that. I don't think Billingham bags do that, quite frankly.
I'm a bit more in favour of hunting bags - if they look like they contain dead birds or fish, that's not a great catch in financial terms.