Re-awakening this thread.
Yes, they are illegal if you're using them whilst riding. But parked, they can't do you in. I fitted mine with a switch so they stay off 99% of the time, and then I turn them on to show mates.
The initial use was to create an extra set of indicators, like what this guy did:
Side indicator tutorial
However, after simplifying what I wanted to do, I ended up using the rest of the LEDs as an underglow like the following picture illustrates. I've spent a little under $200 for the LEDs, wiring, heat shrink, bullet connectors, cable ties, solder, and a soldering gun. The time spent with my bike was just a bonus
My bike kind of has a "bloodied zebra" colour theme, so not sure if I want to make those LEDs go red using heat shrink (used yellow for the indicators, worked fine).