Factory turn indicator flashers are designed to flash quickly if a bulb is burnt out. Unfortunately, the low resistance of an LED looks like a burnt out bulb to these flashers, which leads to "hyperflash". Hyperflash isn't cool.
You can address the problem by adding resistors, or you can replace the flasher. Replacing the flasher is the right way to do it, but it's a little more expensive. Resistors can get hot and they do burn a little more energy. Okay, maybe you're not that worried about the latter. But if you want your car to think it had LED turn signals from the factory, a new flasher is the way to do it.
For the NA, we start with a new factory flasher and modify it. Those factory flashers can actually suffer from cracked solder joints so this is a maintenance upgrade! We know this option is a little more expensive but it takes some time to do.
For the NB1 (1999-00), we have an aftermarket flasher that has to be spliced in. We include everything you need including zipties to clean everything up and make it all pretty.
For the NB2 (2001-05), we have a plug-in replacement unit.
The NA flashers can also be used with incandescent bulbs, they do not require LEDs. The NB flashers are intended for LED use only. Please be aware that if a bulb blows out, you won't be able to tell by the speed of the flasher.
Unlike resistors, which are required at each bulb, you only need one flasher per car.