I'm a lift off style player when playing fps. Laser mice tend to have a really low lift off distance so I would find myself going to turn around and nothing happens. You don't get that problem with the deathadder since it's lift off distance is higher (about 7mm).
I have no jittering when lifting off slightly and moving the mouse. It feels just as good as my original 1800 deathadder and tracks just as smoothly at 5-7mm off the surface. As mentioned above I too use 1800dpi still on the respawn.
Maybe yours dmxdex2020 was just a dodgey one after all?
I also updated to the latest firmware which was released quite recently. Maybe they even sorted it in a release?