Tilden,
These are two different types of software programs. GraffixPro Studio (GPS) is an artwork template designer that allows users to quickly create and enhance existing pieces of artwork to my a final design. Out of GPS, the GT-3 user will click the print button and send the artwork to the GT-3 printer using the GT-3 print driver.
With Digital Factory Apparel - Brother Edition (DFA), the GT-3 user can take artwork that is created from GPS or other graphic software programs and send it to the GT-3 printer. Thus, DFA is a printing / workflow software. DFA allows GT-3 users the ability to queue jobs easier, print with a larger color gamut because it is not limited to sRGB working space like the GT-3 driver, provides more control over the underbasing and comes with several plugins that help clean up artwork. DFA is a queue based system that allows users to setup templates so when the artwork is placed/sent to a queue, it will automatic place / size the artwork and then apply pre-assigned settings (amount of underbase, resolution, platen size,...). GT-3 users can create as many queues as they want to customize it for their shop, but the software does come with some defualt queues as well. It also allows for saving approximately 25-30% print time when printing at 1200 x 1200 dpi (using settings 3/6 or higher in the driver) by using a 2-pass print technique (i.e. pass 1 is 600 dpi underbase only and pass 2 is 1200 dpi highlight + CMYK) on a GT-381 printer.
The best advice I can provide to you is to watch this 9 minute video -
Digital Factory Apparel Brother - YouTube. If you like what you see, then you can download a 30 day trial from this link -
Digital Factory : Introduction. It is a fully working trial that will allow you to send jobs to the GT-3 printer that you can sell to customers (i.e. there is no watermark). This will allow you to see if the improved workflow, pre-designed templates, larger color gamut and more underbase controls can improve your GT-3 business. If it does, you can contact your GT-3 dealer and ask them about pricing.
Hope this answers your questions fully. If not, feel free to ask more questions. If you try the DFA software out, post your comments / questions.
Best wishes,
Mark