Let me reword what Mindwipe is TRYING to say: you should probably get GIMP because it's not only better, but also EASIER. Trust me when I say that, once you get used to the new paintbrush and pencil tool options, you'll save time by using GIMP. Even more so if you learn to use the other features.
Plus, the smudge tool at 100% Rate (an option for it) can be used like the brush tool - you know, where you color-picker the color you need for that section of the eye - without using the color picker.
It also makes it easier to clean the image afterward, as sometimes things start to look...jagged, due to the nature of pixels. You can use the smudge tool at a lower rate percentage (I usually use 30% or so) and smudge out the jagged spots, blending them in with the rest around them.
It's your choice whether you get it or not, but I highly recommend it. Don't be intimidated by the learning curve though, since all you need to really learn to mimic what Paint does is the pen and pencil tool with the new, simple, but useful, options.
Anyway, if you're unsure about your manip quality, feel free to upload them and we'll take a look. No harm in that, since if they don't quite meet standards, we can always remove them. And if they do, we can always keep them.
Also note that, if you're ever interested in learning a little more about manipping eyes, feel free to approach Mindwipe or myself, and probably MMD (Lost+Name, I call him MMD because I can :P) if you're interested in manipping more than just eyes, since those are our respective specialties.