We are pretty big fans of the Burris Ballistic Plex in our home. I have Fullfield II 3-9x40 on two rifles currently. One a Browning Abolt in 7mm-08 and one on my Knight Muzzleloader. Been extremely reliable and usable. The Hash mark values are meant to work based on the "highest magnification" of that scope. So...they work on 9x, but the yardage is different for the related hash marks on different powers. But my son missed a large buck a few years ago because he didn't remember to move his magnification to 9x to use the hash mark. He missed completely and we both still argue over who's fault that was. Considering his age, it was MY fault.
I have been using the Strelok app, and find that tool very helpful calculating the various hash marks at various magnifications. Been really handy.
I will be putting my Burris Signature Select 3-10x40 on my new Muzzleloader that Santa is bringing. That scope was awesome on my 7mm Rem Mag for years, but has been sitting idle for a couple of years now. Excited to put it to use.