So after another week with the M5 front sway bar on my 535xi i still love them. Its the best sub $300 mod i've done to this car hands down.
I find myself cruising on the highway way above my normal speed now because the car just feels so much better. It went from a butter knife to something much sharper now.
Zero negatives to report.
I'd say just do it for those on the fence. This is a nice DIY project if you have ramps and a ratchet set.