I think you only save $20-$30 by getting the butterfly with the frame rails. My reasoning was if I'm not happy with just the rails i'll give the butterfly a shot and only end up paying a small amount more.

My car is a budget track car mainly so i hesitate spending any significant amount of money on it. That being said the $160 for the rails were definitely worth it. Makes my suspension setup more responsive and predictable = safer on track IMO