The only downside is the legalities, DOT, and state laws regarding the distance between turn signals, in most cases I believe it's 8" between them. Also personal safety from a cager whom can't see/tell the difference.
Odds are you'll never get stopped or ticket, but.......
The PreGen Ninjette taillight modification is just barely illegal, but in most cases unless the officer has a tape measure it's fine.
With any LEDs the problem is brightness, and the difference between tail Vs brake brightness, I personally have 80w CREE LEDs in my taillights, and rear turn signals, they seem to do the trick. As an added bonus I also installed two small red CREE LEDs in the bottom two holes in the plate, and the brake light modulator helps a lot. I also added a red reflective NINJA decal, and a small red reflective strip, due to with the DIY fender eliminator also eliminated the reflectors.
ZX-2R Custom graphics.
Otherwise very cool, and a great review.