What are the main differences between this Matco and the comparable KRLs?
Like others have stated, trim and castors
but, it's really not a fair comparison between a KRL and a 4S. 6S? Yes, that would be a little more fair.
I'll take it a little farther. The finish of my 4S is OK. Better than a Waterloo or Craftsman. As good as Snap-on? I don't think so but I'm sure some would argue. More power to you.
Less drawers (oops! I forgot it's spelled "draws" on the internet

). My KRL has 13 drawers for about the same footprint as the 4S. After having a 4S for a while, I'm not real high on it. I prefer the Snap-on drawer layout and construction. The Matco has hemmed drawer edges, but not like a Snappy. They protrude into the tool storage area of the drawer and take up space. Is it stronger? I dunno. All I know is the Snappy drawers have hemmed edges that don't kill space.
The drawer slides are of a lower capacity on a 4 series, but still very nice.
The adjustable detent feature works well.....but I hate detents. I'm a lock-n-roll guy.
The wide top drawer has a stiffener in it that really screws up my toolbox chi.
The 4S is overall a good, solid box. They don't offer a lot of options or accessories for them like the 6s, but they're about half the price of a 6S too.