I'm a lawyer, so I've had to take the bag through security a number of times. It's pretty annoying. Often, you have to hold up the line to unbuckle the bag, unless you're able to do so in advance. Then you have to put the bag on the dirty conveyor belt. Then you have to put the computer back in and rebuckle the bag. If the prospect of doing that every time you fly doesn't faze you, then I think you'll be fine with the Westminster 3. I just keep a laptop sleeve in my middle gusset, and it protects the computer just fine.
I'd go with Classic Luggage to purchase. SAB seems cheaper, and technically is by a few dollars, but they're much harder to deal with, and the customs charges are annoying. Plus, you get to support a local retailer.