Whats the appeal of that style of box?
TL;DR - Cause I really like them both.
If you mean the taco cart, it has a lot of things I like. It's built like a tank. It may be the most robust box Snap-On has ever built. The KR1000 might have a claim on being as robust, but nothing surpasses it.
The layout works really well in my garage. The shorter end drawers are a great place to store things I want quickly when I'm in the house. Screwdrivers, nut/bit drivers, adjustable wrenches, cutters, etc. The front drawers are large enough to be useful without being so large that every drawer is a cavern of stuff to look through.
The rear cabinet for consumables is useful since my garage storage is mostly open shelving, and it's really big (4 doors, but room for about 5-8 vehicles). I don't have to hunt for brake clean, lubes, solvents, etc.
I actually prefer good friction slides to BB most of the time. I don't have to worry about detents or locking mechanisms. A partially open drawer stays open in the position I leave it. The slides are smooth, quiet, and predictable.
Last, it was available at a smoking deal right around the time I was looking for a used SO box.
If you're talking about the top box, it's special because it's the biggest top chest available in the same vintage. The KR-550 and KR-650 are the closest good "mate" to the KR-562. I think when new, the KR-562 was paired with a road chest for the top.