Coming from a battery modded G305, the model O- was an immediate positive change, much greater than I anticipated. The most upfront differences are the weight and the 100% PTFE mouse feet, which glide so nicely (first time trying out PTFE feet on any mouse). Being a claw/finger tip gripper this mouse feels great and its made flicks much easier/accurate including more precise fine movements. Out of the box they come with the new ascended cord along with updated packaging to help prevent any kinks in the mouse cord. Instructions inside on how to change various light settings on the mouse by holding down combinations of mouse buttons (RGB on this mouse looks awesome and sharp). Optional software if you want to further customize (lift off distance, remap buttons, macros, debounce, etc). A couple minor CONS:
1) Scroll wheel very slight squeaks when you scroll quickly. I tend to prefer slightly tighter scrolls but not a game changer compared to the rest of the positives
2) Ascended cord being so super light, large flicks on low sens gaming can result in the cord getting in the way of the mouse. I try to remedy this by not allowing for too much cord slack on my desk but this could be a general problem for any similar mouse that's been paracorded.
Otherwise I would give this a 5