Opening the mouse is again, an easy task, since there are only 4 screws under each pad (yah, they're a bit arcane in their shape, but that's nothing a proper screwdriver set can't fix). Once split in half, the main-PCB stands on the bottom, while the smaller one is strapped to the top half, held in place by two small screws.
The main left & right click-switches are the SteelSeries proprietary ones, which have a very specific click, and feel slightly mushier than the OMRON D2FC-F-FN ones. The ones attached to the top half are the HCI switches used for the sides. These require quite a lot of pressure to be actuated, and give out a fairly audible click. Alas, they're not the most durable ones. Like the Rival, the center and CPI button are TTC micro-switches.
The heart and brain of this mouse is the 48Hz Freescale MC9S08JM32 MCU, a 8-bit processor with up to 60KB on-chip programmable flash memory, 4kb on-chip RAM, and 256 bytes of USB RAM. This is the exact same MCU used on the original Sensei.
Regarding the sensor. Pixart purchased the Avago ADNS 9800SE sensor, yet at heart, there's no difference between the two. This is the same 8200DPI, highly customizable sensor of yesterday, with the same faults and features.
Lastly, we have the battery. Here SteelSeries, uses a Li-Ion battery back, rated for 3.7Wh, or 1000mAh. The leads are firmly attached to the PCB, which means no easy replacement, unless you add some fair amount of DYI into the mix.