I use one of the Wilson Combat backup sights, and it works fine. I wanted to set up my rifle so I could use either the carry handle or an ACOG or EOTech with BUIS, depending on the situation, without having to re-adjust the front sight post. My upper receiver is a Bushmaster, so the sights are a slightly different height from the Colt ones most BUIS are made for. The Wilson Combat sight was the only one I could find that allows the elevation to be adjusted to compensate. (I realize this whole issue is not relevant to everybody reading this.)
The elevation and windage adjustments take so much torque to turn that it is unlikely that they would be "knocked" to a different setting. It takes about three to four times as much torque to turn either knob as for the windage knob on standard A2 rear sights. Also, the knobs don't stick out a whole lot from the surrounding structure, so it would be fairly difficult for a random bump to hit them.
The sight has a single aperture that is slightly larger than the small aperture on standard A2 rear sights. I haven't observed any noticeable change in accuracy as compared to the carry handle sights.
If you don't ever plan on switching the sights around like me, elevation adjustment on the BUIS isn't really important. Some sights of different height (like the Bushmaster ones) may cause the front sight to require adjustment that makes the wide part stick out of the base. Bushmaster sells a taller front sight post to alleviate those issues.
I hope this information is helpful.