I have no experience with PrintFab and I don't know what you mean by more flexibility in using inks. What does it bring to the table that your printer driver doesn't do well?
It, like some other RIPs, allows you to get more use out of inks the driver underutilizes, such as the O and G inks in the Epson 4900/7900/9900. Not a bad thing given the Y is most vulnerable to fading.
PrintFab also bypasses the artficial length limits imposed by the driver on printers like the Epson 3880, which won't print longer than 95 cm through the driver. I don't know if it gets around the borderless limitations on sheet sizes - if a printer can do borderless 8 x 10 inches, then there is no physical reason why it cannot do borderless 8 x 12 inches.