Let's take a look at the hardware inside. First of, I should note its easy to split it apart, with only 2x screws hidden behind the rear PTFE pad and two clasps at the front.
The PCB is of quality build, neatly arranged, and with proper soldering.
Castor uses a 32-bit ARM Processor, the 32Mhz STM32L100 that included in several top of the line gaming mice, including Logitech G502. It features a 10KB RAM, and 128KB on-board ROM memory. Centrally placed, you have the PMW-3310 IR-LED sensor - with a DPI range of 100-5000DPI (Castor ups the resolution via firmware to 10k), and a tracking speed of 5.45m/sec (215IPS), improved again via firmware.
Left and right click are represented by OMRON D2FC-F-7N mechanical switches with a rated lifespan of 20-million clicks. The scroll-wheel encoder is of TTC make, a decent choice at the very least.
The top panel holds three micro-switches for Back / Forward & DPI buttons - two of which are TTC Red (rated with a lifespan of 4-million clicks) and one TTC White (6 million).