While the Vault has no app, we do have a mobile version for the site that can be accessed regularly from your browser of preference while on mobile. Personally, I think that the mobile version is great for reading blogs and keeping updated with the rest of the site, but for character builds and posts with too many pictures, I would say that it would be better to scroll down to the bottom of the site's page and click on "Full version". That way you can see the site like you would on a desktop, which could be useful if you're having trouble with the mobile version.