Grenade Grips are like Fat Gripz, except way cooler on account of the fact that they are (loosely) shaped like grenades. At least that's what the people who make them would have you believe. If you're looking to increase the difficulty and cumbersomeness of pumping your barbells, dumbells, kettlebells, and cable ropes, one probably works as well as the other.
By "works" I mean that thicker grips on these common pieces of equipment are intended to recruit more upper body muscle fibers, and get your arms ripped faster. Grenade Grips also support athletic performance, strengthening hands and arms for pitching, bowling, climbing, grappling, and swingin' an axe. With continued use they say they'll also lessen common joint and tendonitis pain since your increased muscle strength will reduce the loads and stress you would otherwise put on your joints and tendons.
Grenade Grips come in Army Green (obviously) and Hot Pink (also obviously).