That train is as sweet as it can get, but 3 suggestions:
- I suggest going for all images being 64x48 or more (I see that one is 52x48)
- Don't cut any transparency: I see that left and right the transparency is cut, and that is a bit visible and unpolished (I know it is very frequent, and sometimes I do it too, and I don't like it).
If cutting any transparency, I suggest to keep an uncut version in the folder, just in case.
- I suggest providing an alternative "units" folder, with the units images without the flags, especially (but not only) if the flags are not the only way to tell them apart.
Ideally, the unit flag should not be part of the same image, but should be a different image, and the engine being able to associate them, so that you don't need to paste the flag into each single image; it would be cool if a developer can do that (the current Flag Display Mode is not good enough for that; so, I agree with having it in the image, as you did, with the current engine).