Wade:

I've used both a flat spokeshave with a rounded nose (see Lee Valley's spokeshave) and an inexpensive convex unit. As far as quality, the L-V is a nice shave, but it's usefulness is limited for rairing. I found that among the areas of the hull I couldn't get at with the block plane, there were few areas that the flat L-V spokeshave could help with. I picked up a cheap Kunz convex spokeshave at woodcraft (about $15). It was useless until I sharpened and flattened the meager blade, smoothed the bed and mouth, and cleaned up the overspray on the blade holder. I was able to get servicable results with it after that, especially in the hollow areas of the stems. I practiced on some scrap to set the depth of the blade and get the feel for the proper angle of cut. Any imperfections sanded up nicely. I think it was worth the effort, but it is not a perfect solution. The alternative for me was to fair those areas with sandpaper; and I just chose to try the spokeshave.

I guess what I'm saying is that: it's a useful tool for some applications, but be prepared to do some work on most inexpensive spokeshaves to get them to work well.

Enjoy!