I have the Sensei. Great mouse. If I were to get another mouse from them I would get the Kinzu or Kana. Sensei is very nice and light but for the price I would rather get a Kinzu.
Note that the old Razer software wasn't that great either. You would have to restart your computer when you changed profiles or messed with settings. At least thats what happened for me.
The Kinzu has a horrible sensor, just so you're aware.
I find that the old Razer drivers are better than most other. They felt a bit clunky initially, but I never had to restart to change settings, only to install/uninstall, but plenty of hardware drivers make you do that. I've found the Razer driver interface to be fairly neat, at least compared to Logitech drivers.
As for the Ouroboros, it's physically interesting, not sure about the sensor but Razer seems to have started using decent ones again, but the wireless + Synapse 2.0 is really putting me off. If it was either wired or didn't use Synapse I'd probably consider getting one, but not when you need to deal with both.