Interesting... Several of the initial detailed reviewers say that it crashes a lot, has a pretty difficult to use interface, and has an impoverished database of points of interest.
Some additional information on the app is provided on their website:
http://xroadgps.com/Maps/GMapforiPhone/tabid/2463/Default.aspx
PS its total space consumption is 930MB... that's not very large, but considering it only has partial coverage of half the US, it would seem like it should have better POIs (and/or integrate with Google Maps or another resource to supplement itself when network access is available).
PPS it shows up as $19.99 USD for me presently....