Well, when it comes to the sensor, SteelSeries Sensei Wireless uses the Pixart ADNS9800SE laser sensor, capable of reaching up to 8200CPI. 8200CPI is an impressive number, the kind that wouldn't be used by the majority of users, gamers or otherwise. It's also one of the most popular laser sensors to date, with so many using mice using it, I can't even properly list 'em.
There are some drawbacks to it. It has slight negative acceleration and latency, but that might actually be slightly different with the newer iterations, and firmware updates. From my experience with the Sensei Wireless, I cannot say there are visible tracking issues, and whilst I feel that my G520 behaves a bit better on the pad, I don't think the Wireless' implementation of said sensor warrants the proper set of tests, since it behaves pretty much the way I'd expect it to.
Other than that however, I cannot say I have an issue with Sensei Wireless. I've had the mouse for about two weeks now, and I got used to its shape pretty quickly, even though I am primarily a palm-grip user, who likes large & flat rodents, like the G520. It has the appropriate size, catering to everyone, though dedicated to none. Honestly, if you've never subscribed to the idea of a grip-type mouse, then Sensei Wireless shape and design is perfect.
Day to day use
This is difficult to entail because I don't know who'd buy this mouse for office work. I mean, it's clearly catered to the gamer audience, though the more sensible one that likes subtlety, and no flashy edges and ridiculous designs.
However, I do see a point to the SteelSeries Engine being used to shorten one's workload. It can provide almost everything an user could need, for any application that uses 8653 shortcuts.
Lastly, how does Sensei Wireless behave while gaming? Quite well actually. I think there still is some acceleration issues with it, though most assuredly not as much as another Avago 9800SE mouse I looked at, the Corsair M65. It's quite close to the 9500, the other laser sensor, who also had some issues when it came to acceleration. What I mean by this is simple. If you are looking for a 1:1 response ratio, then you could look at other rodents, like SteelSeries' much cheaper Rival, or Logitech's G502. However, if you don't actually notice a difference between one or another sensor, then Sensei Wireless might just be for you.
When it comes to the Wireless bit, here is where the mouse truly shines. There's no wireless mouse that I'm aware of to match the performance Sensei Wireless has. Between using it with a cable and using it without, there's almost no difference. I did not notice any latency, even in a interference laden environment, nor did I notice any erratic behavior. This is by far the most stable wireless experience I had with a gaming mouse so far.
The battery life is also quite good. I used the mouse full out, without caring for the battery. We didn't get the sixteen hours rated by SteelSeries, but a nice, safe 12 hour runtime, which is actually better than Gigabyte's Aivia Uranium, who used two 2100mAh AA NiMh batteries. It doesn't even come close to Logitech' battery-saving, always wireless G602, but for what it is, and its battery capacity, Sensei Wireless has an overall great battery life.