As about one half of the instruments I have built have been carved top and backs, convex soled finger planes are a necessary tool for graduating the thickness and the smaller ones do work very well in shaping braces. But as I stated before, they are easy and cheap to make. I have made many of them and they seem to work as well as the expensive cast bronze ones. The secret to keeping the cost down is making your own blades. As it happens, I made custom knives before I started building instruments. If you have a reciprocal saw (Sawzall) and some old used saw blades you can make them at no cost, and even if you have to purchase a couple of Sawzall blades, you can make the finger plane blades for less than 1 dollar apiece, which is considerably cheaper than the $25 per blade for the Ibex planes. I have taken some pics of me making a blade and will post a link to them shortly. I think the process will be fairly self explanatory but I will offer a couple of pointers then.
Brad