It's a shame, because it's the one feature that I think undercuts what's otherwise a solid gaming mouse at an amazing price point. But these thumb buttons should never have made it past testing—the edges should've been rounded more, or brought closer together.
The Rival 100 is a solid choice for people on a budget, but honestly the jump from low-tier to mid-tier to high-tier is a lot smaller in mice than in other peripherals. Most of the time you can find the Razer DeathAdder on sale for only ten to fifteen dollars more, and it's a huge improvement. Or the Rival 300, which lists for $60 but can typically be found for less—and is, again, an improvement over the Rival 100.
But if you absolutely can't stretch the budget further, the Rival 100 is a pretty good option. It gives you the bare necessities for a gaming mouse (an accurate sensor, moderately high DPI range) without compromising too much on comfort and style.
Just take a bit of sandpaper to those thumb buttons.
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