This is an excellent initiative that we owe to Dominique Gauthier : iTabNav.fr is a new French e-commerce website mainly dedicated to iPad (and iPhone) accessories useful in’marine usage of these devices.
Rather than looking on Google for e-commerce websites overseas, you can now go to a French specialized website. Dominique Gauthier did not hesitate to raise my opinions on the technical aspects of his choice of accessories, being himself user and boater.
iTabNav.fr has been open for a few days, his catalog is gradually enriched, I welcome his initiative and wish him good luck.
The application is integrated. Yes; GPS position is displayed. Read that article on comparative vs. Navionics Mobile iNavX Navionics.
Your question surprises me : it seems to me to write extensively on cartographie Navionics in this blog, and I have detailed from my website the use of the application that uses this mapping iNavX, among others.
Navionics Mobile on the application which can be bought directly from the AppStore, I recently completed a comparison with iNavX that may enlighten you. I'll upload some screenshots on the Caribbean.