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Corsair has -- hands down -- one of the best mice on the market with the side button design.
What sets this one apart is the key slider system, which lets you re-position the buttons on the side to fit your grip.
The side buttons also have textured grips to help you distinguish the feel of each button and ensure precision.
If you love this style of gaming mouse with the buttons on the side, be sure to also check out these models: