I toggle between 4 DOF and 6DOF (disable/enable X - Y) , depending on the situation but particularly in combat. With Freetrack you can do this by assigning a key to the hat switch and it's an advantage to be able to switch between 4 and 6 dof.
Unfortunately, TrackIR doesn't have this feature. I suggested on the Natural point forum that they include this at some point but they said no! NP maintained that users would not want this feature........
I sold my TrackIR Ultra - give me FT anyday with its assignable axis (all six are assignable along with centre and pause!