Hey Tommy -- a couple clarifications if I may...
The DPS Preflight app (it's in the App Stores) is one way to proof content (articles, banners, collections), cards, and layouts. You don't need to share this app, just have the other person download it. Once installed, sign in -- if your AdobeID is part of a project and has one of the permissions in the Content section enabled, then you'll see the project in DPS Preflight. If you're part of multiple projects, you can select which project's content you want to see.
If you're part of a project, but you don't have one of the Content permissions, you will not see the project.
If you are the master or have master admin access, you can see the project but cannot view the contents of the project. (There's a message to this effect.)
OTOH, if you build an app and enable preflight, you're making a custom preflight app (with your icon/splash and custom font support.) -- And you'd have to include the UDIDs for all testing devices in your mobileprovision file used in the app signing process.
Both DPS Preflight and a custom preflight app view the content in a project after you click the Preflight button in the Contents & Layout area. Wait for the progress bar to finish, then change views in the app to see the update message.
HTH -- Colin