It isn't very common on these bikes for couple of reasons, mostly having to do with light output and power consumption.
They're small individually and have small reflectors. That's fine as long as both lights can be made to operate simultaneously, but in order for that to happen you'd have to use lower wattage bulbs in both because our charging systems won't support 2 55/55 bulbs. On a late model bike you could probably squeak by with running two 35/35 bulbs.
The other option is to wire them to run solo, one "hi" and one "low". But a 55/55 will cause some of their plastic lenses and housings to melt down. Many of them were designed for 35/35 or even 25/25 bulbs so you gotta pick your housings carefully.
They're cool, but be aware that even a 60 watt bulb wired individually with such a small reflector isn't likely to perform as well or give as much coverage as a 35 watter with a stock reflector.