I like the "Groucho" light a lot. It's a single half-watt LED. The Groucho light does not blink, so you get the full half-watt output at all times. By comparison, the top "bright" LED in a PBSF is also a half-watt, but it's also off or dim most of the time. Of course, it's nothing compared to a DiNotte's three watts (or thereabouts).

Remember, the Groucho light not a battery-powered light. It requires a dynamo, and it is unswitched. I use a hub dynamo and a Schmidt Edelux headlight, which provides power connection and switching for the taillight. FWIW, I like the ambient light sensor on the Edelux. It switches both lights on under bridges, in the long shadows after dawn and before sunset, and on heavily overcast days.

I was fine with this one for the intended purpose of side visibility and legally-required reflector. The Groucho light is brighter--a noticeable amount, although not an order or two of magnitude as with the DiNotte.