I have them on my BMW and many BMW and other touring bike have them. They are quite bright and really stand out in traffic. I ride the yellow lenses. They are not so bright as to blind anyone during the day but would at night if you don't turn the brightness down with the included weatherproof control knob. Even tho my BMW has a 10K lumen LED headlight, the 2x2000 lumen yellow Darla's really made quite a noticeable difference in terms of people turning in front of me. I've only had them a couple weeks. They are pricey.
If you installed them or other running light, where did you put them. I don't have, nor do I want, a front rack to mount them to.
Clearwater has a version with a single light mounted to the Vespa front shock cover - see below. While it is probably effective, I think you really need to have the light or lights a bit higher up to get the most attention. Especially so because the wheel will block its glow on the right side of the bike. The Vespa GTS/GTV 250 may not have sufficient electrical capacity for two lights (24 Watts for each light) but certainly will power one light if you converted you GTS/GTV headlight to an LED (I did) and it conserves about 25 Watts. If you convert all the incandescent bulbs to LED, you can save another 20-25 Watts. I also don't like the aesthetics of the LED mounted to the front shock cover. it just looks pasted on.
I wondered aloud to my self about retrofitting a Darla on top of the GTV fender light or in the horn cover. Thoughts? I'm just kicking this concept around and interested in other's opinions.
I started down this path a few months ago when I saw the Darlas on a BMW, two cars behind me at a stop light. He was unmistakably conspicuous. I put the car in park and ran back to ask what they were and had been eyeing them ever since.