I was lucky enough to have a lot of experience with FreshGrade in my classroom last year. It was an awesome way for the parents to see into the classroom and what their children were doing in school. Every couple of weeks, my teacher would bring the iPads into the classroom and the students would take pictures and some videos of what they had recently completed, or what they were working on. They would add comments onto their photos to explain what the assignment was. I found that it was a great way to keep students in the loop, and the students seemed to love doing it as well! I think it motivated them to do a really good job on assignments because they knew that they would be sharing it with their parents or guardians!
I haven't heard of SeeSaw but it sounds like a great resource as well.