Thanks for the post. I have a fair number of boards I need to thin down (making some bee hives) and this looks ideal. I've a couple of suitable, old planes knocking about as I've picked them up for pennies in boxes of tools in house clearance sale.
Hit Youtube with the term Scrub Plane or Using a Scrub Plane and there's a decent bit of info but the main point is the very open mouth and heavily cambered blade.
I do have a few fairly posh planes and a surplus of sizes but there's really not much to scrub planes. For me its not worth spending a hundred quid on one.
As Paul Sellers points out in one of his excellent videos many old wooden coffin style scrubs are actually just a worn out smoother where the mouth is too big for effective smoother usage.
You don't need much in the way of adjustments on them either.
Put the plane on a flat surface, drop the blade in til it touches the flat surface, tighten it up and then give the blade a tap at the back so its sticking out slightly.
With an old No4 you will likely have to attack the front of the mouth with a file or it won't allow the bigger and thicker chips through and it will jam up.
Obviously with a 4 you have a thumbturn knob to set it but the lateral adjust lever will be mostly redundant because the large camber of the blade.
Just remember, you don't need to be spending Veritas type money on these things. Its just a rough plane with a very open mouth and a heavily cambered blade.
You're not going to be jointing tabletop boards with them so extreme flatness just isn't needed. Also a wider blade isn't always an advantage because you have to push it through the cut with a deep setting.
Personally I chamfer the edge thats away from me so it doesn't spelch out and do diagonally across the board where its needed and then maybe diagonally the other way before moving onto a jackplane/jointer or smoother depending on what I'm on with making.
I have recently been getting a few wooden planes as well, wbicb for years I avoided like the plague but surprise surprise, I was wrong. They can be surprisingly good and great value.
I'll fire up a few of my findings with those when I get time.