TomD
I wouldn't adjust a mouth with a float that has the heavy teeth, so you can toss that expense. The Japanese ones might be excellent, but anything will work. Sandpaper on a stick. I use mill bastard files, or the ones with the cross shaped teeth that cut faster. I use a chisel if I need to open the mouth a lot. If one is doing a resaw/glue type plane I mill to finished surfaces, dry assemble and pin, then I glue it up. That will get me to where a file will work. Remember that most planes work better with an open mouth. All planes work better with the most open mouth possible.

The reason floats are used in plane making, reamers are used in hole making, etc... Is there comes a point where the amount of material that needs to be removed is sub what a more free cutting tool can easily accept. In addition these tools "mold" whole surfaces. So a plus 1 thou reamer will ream a whole hole to that dimension, a float will level a whole surface. For a mouth a file is just dandy.

Hey Pam or Dave, had either of you heard of Japanese floats? In thirty years of making and reading and watching everything on Japanese planes, and attending two master's seminars, I never saw or heard of a float for those planes. That would have made stuff a whole lot easier. In fact, with the right float, there would be little reason to scrape the sole for the wave pattern.