Run an AE spur gear, and pick up AE's VTS.
Cheaper, and more readily available.
I have both the VTS and an Avid, albeit no in an RB6 (B4, SC10 and B44). They perform the same, but the Avid is considerably more expensive, and harder to source parts for. You're also limited on spur gear selection with the Avid. VTS sits inside the hexagonal recess in the spur, so you can mount it to any AE style spur.
I've found that the multiplate slippers help put the power down smoothly. A traditional slipper transfers power abruptly. It's either slip or grip. The VTS makes the transition smoother, so you can start putting the power down sooner. It helps keep the car from getting too squirrely on rutted up tracks as well.