I purchased the Flush Plane several years back and it just keeps being a stellar pinch hitter in my shop.
The system is essentially a molded plastic handle with a rare earth magnet on the base. It securely holds onto what would otherwise be a naked plane iron, letting you lay it down on the flat and perform paring duties. The shape and index pin location are pretty much proprietary to just this flush plane.
So don't expect to use the handle with any other iron you may have laying around. But since this is a handle AND an iron that shouldn't be an issue at all.
This tool straddles the line between a chisel plane and a cranked-neck chisel, but without many of the downsides that can arise with both. The blade skates on the surface of your project, allowing full access of the cutting iron to get into corners or to do other flush paring duties. It can get right into spots that would be difficult to get to otherwise. And there is no handle to get in the way.
The rare earth magnet, an indexing pin in the base and molded rear edge all help to keep the iron in position as you use the tool. When done you can remove the iron and flip it over, protecting the cutting edge from damage.
I use this tool a great deal when trimming veneer edges or when I need to get right into the corners of things that may need a little attention. The two inch wide iron is big enough to tackle many different situations, but it's not so big that it's cumbersome at all. Best of all, because you're registering the entire base against your work there is really very little opportunity to create an accidental dig, as you can do with a cranked-neck chisel.
Sharpening is done the same as any other traditional plane iron. The sides of the iron are parallel to one another and are 90° to the cutting edge. So being able to keep a keen edge on this tool is very simple and straightforward.
It's definitely not a tool that I reach for every day, but when I need it I *need* it. No other hand tool in my arsenal is capable of doing what this flush plane is capable of.