Never used a US Pro box, but it looks nice. However of course, looking nice and being ncie are two different things - my Halfords box and Machine Mart boxes both looked nice, but were the most useless pieces of shite ever conceived. Ok, possibly a little harsh agains the Halfords box, which wasn't THAT bad, but the Machine Mart "Clarke" box was fucking dire, and I should have returned it the moment I took it out the box! About as rigid as a wet cake!
Snap On boxes are expensive, yes. Can't comment on the new ones quality - mine is gotta be pushing 20 years old at least, and still going strong. It's lived on vans for the past ten years (how long I've had it), and taken a lot of abuse - had it's lid removed, handles removed, had various holes drilled in it to bolt it down, got wet, been stood on, doors slammed into it, been used as a worktop bench for hammering, etc, and it's still bob on. CANNOT fault it. It's the only box that's lived up to the rigours of road life, and I'd not hesitate to buy another.
Would I buy one for sitting in a garage or shed and being used at weekends? Probably not. And there are cheaper alternatives for daily pro use that will be fine for static duties in a workshop, you don't NEED a SO box for that. I disagree it's about willy waving - usually that's said by people that want them, but can't afford them.
The other thing you have to remember about SO, and other brands like them, is the aftercare. We all know SO's no fuss exchange/replace/repair for tools, and this extends to their boxes too. Drawer slides break? SO will send you a full set of replacements, and charge you nothing. And you know you'll be able to get service backup for decades and decades - something you won't get from companies that discontinue their models, change their line up, etc. Try getting spares for a 20 year old Halfords tool box - I bet you can't!
As I said in another thread, I'm not a SO snob; many of my tools (the majority infact) aren't SO. But when it comes to boxes, nothing else comes close, and I wouldn't buy anything else, especially for life on the road.