Has anyone tried to use an ereader with their maps ?

I have an Astak 5" pro ereader. I can use it to view pdfs and B&W bmps.

I looked at both pdfs for a guide to Castle Riche-Guet. I could see them, but since I am not used to viewing pdfs on my ereader, I couldn't zoom in.

I get the impression, but I could be wrong, that pdfs larger than 40 columns wont work with my ereader.

What are your experiences with ereaders ? Have you used one to take maps and adventurers to a convention, etc. ?

Thanks.