It's just a beefier version of the stock sway bar. I didn't drive my X enough to really compare A/B, just went by my M3P experience. I've read people here swear by this sway bar being a great upgrade for the X. There are 3 settings, I put it at the stiffest.
The Unplugged Performance 2021+ Model X Plaid 3 way adjustable rear sway bar is a suspension upgrade developed on the track in conjunction with Randy Pobst. The sway bars are an easily felt upgrade for the Model X Plaid's handling, as you'll experience the improved chassis balance and tracking...
unpluggedperformance.com
These go on sale occasionally, There was a big deal on black Friday, I ordered a few days too early. Add about $200 for installation if you don't have a lift.
Edit: I just read the review in this link for the 1st time. I agree 100% with the reviewer that the comfort level increased on my M3P due to the car being almost 0 unsettled on rough pavement. Probably some of this carries over for the X.