emprex is also known as BTC. They make all kinds of pc peripherals usually sold at frys. My emprex DVDRW is actually a very nice unit, very quiet compared to a lot of "name brand" versions.
the internals of the mouse are probably the same parts as MS or Logitech. I bought a BTC clone of the MS optical explorer mouse back when optical was new. It's still running strong though the teflon pads are coming off.