Tom, the scraper shave has a brass toe in front of the blade. Behind the blade is the machined steel. The surfaces are all in the same plane (ie dead flat). Similar to the Bowyer's edge in that regard. The BE has the solid brass toe and then a brass plate inlet into the wood behind the blade.
RD, I think most of the bowyerin' I've done has been with a scraper shave. I'll rough things out with a drawknife or spokeshave and then switch to a patternmaker's rasp and the scrapershave. The scraper shaves are great for bringing a bow into tiller.
Spokeshaves can remove much more material and you have greater control than with a drawknife, especially if you're not used to using a drawknife. I nearly cut a bow limb in half roughing out a bow with a sharp drawknife!
If I were to get only one spokeshave for bowyering it'd be a low angle spokeshave. These do great on wood that doesn't have a lot of figure. Quality wooden-bodied shaves range from $90-250 depending on the make and features. Or you can buy the blade kit from
Hock Tools and make your own. They have instructions on the site. Veritas makes a
low-angle spokeshave that looks great, but I don't have one - it's next on my list to purchase.