If you're serious about PC gaming, you've already heard of . You might remember its first high-end mousepad (excuse me, "mousing surface"), its , and possibly even its highly acclaimed Xai gaming mouse. Lately, SteelSeries has been releasing lots of licensed gear such as its , but with the Sensei, it's going back to its professional gaming roots. This mouse is intended to replace the Xai, which means it's only for the best of the best. (Of course, the $90 price tag already told you that.)
With the Sensei's processor, you can tweak every single mouse setting you could possibly ask for. A major feature is fine control over mouse sensitivity; you can tweak the mouse's actual hardware counts-per-inch (CPI) sensitivity from 1 to 5700, but if you want to go higher than that (maybe because you work with multiple high-resolution displays), the processor and built-in software can "double" your CPI up to 11,400 CPI. In practice, I don't need to go over 3200 CPI or so while using three monitors side-by-side, and my default is around 1600, so you might not use this feature much.
You can configure individual mouse profiles to alternate between two sensitivities and switch between the two of them by pressing a mouse button located below the mouse wheel. This comes in handy for games and apps where you need instant access to two different settings--"camping" the bomb site in Counter-Strike: Source with a sniper rifle or working with a big spreadsheet in Excel, for example. I find that I sometimes accidentally hit the toggle button, which can be a rude midgame surprise. Fortunately, you can set that specific button's LED to show a different color depending on which sensitivity setting you're using.
You can also control the lift distance and mouse acceleration/deceleration, and set the drivers up to fine-tune (or eliminate completely) any mouse path correction functions. While these features are undoubtedly all really cool, you're probably not going to change those settings unless you're a dedicated hardcore gamer who already knows exactly how they affect your playstyle. I like to think I have some solid PC gaming chops, but I was a little lost when it came to playing with things like lift distance. If the Sensei included a setup wizard that explained some of these settings and how different games/playstyles/desktop setups worked best with different settings, it would be easier to recommend the Sensei to a broader gaming audience.
Like any good gaming mouse, you can configure different profiles for different games and applications with the included SteelSeries Engine driver software, which lets you change the seven button assignments. You can even develop in-depth macros that track timing and include keystrokes, though those probably won't be tournament-legal for your game of choice. Also, you can map different functions to each button press and release, which can come in handy if you need to activate the first half of a macro when you press the button, then aim it at something, and then complete the macro when you're properly aimed at your target. Naturally, it takes a little practice getting used to mimicking your in-game timing in the driver software, but it's not hard to test out different tries until you get it right. You can also track your mouse usage sessions to see which buttons you use more often than others, and change the colors, brightness, and intensity of the built-in lights.