They both use the same optical sensor. I have the Optical and it works great, especially if you have smallish hands, plus it has texturized so it wont slip out of your hand during fragfests. The Explorer may have more buttons; the Optical has 5.
Asus P9X79-Deluxe, Intel i7 3930k @ 4.2Ghz, 16gb DDR3-1600 Kingston HyperX Memory, Coolermaster Storm Trooper case, Corsair AX850 psu, Geforce 680 SLI, Corsair Model H100 w/c, Samsung 840 Pro 512gB SSD, Asus Blu-ray Writer 12x, Windows7 Pro x64
MSI GS Series GS60 Ghost-003 Gaming Notebook 15.6", Intel Core i7-4700HQ 2.40GHz (3.2 GHz), 16GB Memory 1TB HDD 128GB SSD, NVIDIA GeForce GTX 860M 2GB, 4.36 lbs., Windows 8.1 Pro