Some leds have resistors so they draw the same as oem bulbs and retain the flasher interval.
The real problem with LEDS is that they are pretty directional. Keep that in mind - only people directly behind you, on axis, will see them brightly.I guess some now have dispersion patterns of leds to combat this, but I havent seen them in person yet to comment on them. I think sport bike rider did a led comparison that was pretty informative.. try and google it.