I toyed with the idea of wet erase markers, but it seemed like a big mess in the classroom. As of now, I have used the dry erase a few times and have run into only a few problems, none of them could be remedied with a wet erase marker. Now that I think of it, wet erase markers would be harder for students to go back and fix any mistakes that they have made. With a dry erase marker all you need to do is wipe quickly with your thumb and the student can replace his/her answer.
As far as the suggestion to go completely app driven doesn't really seem to be the aim of this app. We have to keep a couple of items in mind. First, most public education classrooms serve students that don't all have access to electronic devices. Secondly, the sad fact is that we are teaching students how to take a bubbled in form for standardized tests. Even though many of us would like to move away from that, bubbling answers in on a sheet is good practice for them.