Worst case, Apple has a 15 day no question return policy. (double check this in case my information is out of date).
I don't normally like the idea of getting a device before I know I'll keep it, but in your case that might be the way to go. Do a little planning, pick a sunny day and give it a test.
Or, if you've got iPad owning friends (or fellow pilots) I'm sure they would make a quick loan.
A picture really isn't going to give you a good idea of how easy/hard the tablet is to using in those conditions. Cameras don't work like eyes. To get a picture of what a screen looks like would require exposing the tablet just right, not automatically, and even then the eye's greater range of light sensitivity means the best camera shot will still under or over play how well your eye will do in the same lighting.
A live test is the only way to go, especially for something as specific as you want.
That said, I've heard several stories of small craft pilots using iPads, so it's obviously possible. The real question is whether it will be good enough for you.