These are not just a wooden shoulder plane. A shoulder plane is expected to take a slicing cut on end grain and usually has a low angle. On the other hand a rabbet plane is designed to rapidly but smoothly cut side grain and thus will have a bed angle like a bench plane. A good rabbet plane will eject shavings out the escapement where as a shoulder plane will quickly clog since it was not designed to cut large amounts of side grain material. A good rabbet plane is a joy to use and a wooden one is light and quick.
To demonstrate I put a couple of videos together to show you how a properly set one will work. First, I I have a left hand side round that I use to set the gage line for my 3/4" rabbit to track in. I have the rabbet plane set moderately heavy. Watch the shavings really shoot out the escapement as I get going toward the end of the video
Now I show a full width shaving that is set on the lighter side for a 1-1/8" rabbet plane. A large rabbet plane like this is nice to have. I find I can keep my rebates level and plum much easier and track my gage line by using my fingers as a fence more easily as well.
These are planes that I made and will be part of what I will be continually offering as my range of moulding planes expand. For now I have these available in my Etsy shop.