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I used an LED 1157 purchased at my FLAPS in my last car's back lights; with an incandescent in the front I never needed to change the flasher. It was a reliable bright bulb but I would not say it was noticeably brighter.
I've not seen them in person but I like the fact that there is a definite difference in brightness between running and stop. Most 1157 LEDs don't have much change, making the brake lights not stand out as clearly as I'd like.
However, they do not address your concern about flash rate. Superbright, among others sell load resistors you wire in yourself but I'd just replace the flasher with one designed for LEDs.
Rezvani's Latest Post-Apocalyptic Monster Is a Ford F-150 Raptor Underneath
Slideshow: Called the Fortress, the 850-horsepower pickup combines Raptor underpinnings with military-inspired features, survival equipment, and a starting price of $285,000.