The screenshot on the right shows the Store screen for the Android app. The button in the action bar can be used to restore any purchases previously made for the current Google Play account, as discussed here. The items in the list below it are the various options that can be purchased.
This option allows the user to back up his database to a Dropbox account, and a free 2GB account is perfectly adequate for this purpose. Vanguard Software strongly recommends that all users who run the app without a web server purchase this option, and use it to back up their databases on a regular basis.
This option allows the user to send a copy of each finished invoice to the customer, and another copy back to his company. This is a very useful and popular option. A Gmail account is required, and for security reasons we recommend that the user creates a dedicated one for use with this app.
This option allows the user to print a copy of each finished invoice. Unfortunately this otherwise highly desirable feature has limitations which make it unsuitable for most mobile sales. The app will only print on A4 or US Letter sized stationery, and the printer must have an internet connection. It is not enough just to carry a mobile phone and a printer. The user has to carry a Wi-Fi router as well.
In practice this option is only suitable for scenarios such as trade shows and showrooms. It will also work with vans that have their own Wi-Fi routers and mains power supplies (these do exist, though they are rare). It works well with HP ePrinters, and it works with Google Print too, though some users have trouble getting this to work.
This option supports Bluetooth scanners which support the HID protocol. This includes most of the scanners currently on sale, which are usually described as being Apple compatible. The Android app still supports camera scanning, but this is a bit of a party trick, and this feature may be withdrawn in future releases.
This option allows the app to be used for more than one company. The database for each company is stored separately, allowing them to be hot-swapped. Since most of the user preferences are also stored in the database, this allows the company to be swapped immediately.
This is just a cheaper way to purchase all of the above options.