Hi Jason, It's done that way because some people like it inside the stab and other on the outside, so it does not matter what servo brand you use.
I got my Osmoses with the internal servo pocket already done and ready for install, but I ordered it that way.
I've been using 3421 on my Osmoses but the metal gear version on the stabs with no problems, I'm a little concerned about the SA, but Marcelos Xuramas has the 3421 on ail and elev.

It's electric, do you think I should be concerned?