I really think that the mobile directories are the way to go. Sadly, our principal wouldn't allow it this year, even though several other schools in our district are using them. I'm not familiar with the company you are looking at, but we looked at
www.atozdirectories.com/, which has the same concept, and really liked them. There was another company we considered as well:
www.MembershipToolkit.com They had a lot of bells and whistles that we weren't really interested in using (or paying for), though.
I should point out that because of the way these companies make money, I think they could be somewhat local in scope. I'm in the metropolitan Washington DC area, and I think the two companies I mentioned only do business in this area. I see the company you mention is in NJ--not sure if it does business outside of that area.