UPDATE: The Strum Fix Plus 2 is available and shipping now!
The Strum Fix Plus 2 features a 'split' strum bar very similar to the one that was on the original Rock Band Fender Bass replica guitar, allowing you to do 'alt-strumming'. (Alt-strumming is method that lets you rock the two strum bars up/down just a tiny amount and still register strums, resulting in very fast strumming with minimal motion or fatigue).
It also allows you to 'pluck' the strummer in a way which more accurately mimics the way a real bass guitar is played. The SFP2 features the exact same switches and centering spring as the original Strum Fix Plus, so it will share the reliability and positive feel of the original.