Thanks, Aus, hope my comment is helpful.
Some more info:
Have just checked my Cygolite, and it's an Expillion 410. It's rather bigger than a Streak, being about 95 mm long, and about 35 mm wide at its widest point. It weighs about 4 oz, sez my antique scale from a Mennonite hardware store.
I bought it at Mountain Equipment Coop in the summer of 2012, just before my first tour in Europe in Sept/Oct of that year. Cost was around Cdn $100. That seemed a bit steep 8 years ago, but the light has been a great bargain.
Its performance has been outstanding, and the light has been troublefree in all conditions--rain, heat, cold, dust--so much so that I never think about it. (My criterion of excellence for just about everything mechanical.)
One handy feature is that there is about 25° of float in the mounting, so that I can easily push the beam off to my right or left when I'm approaching another cyclist or a pedestrian on a bike path, and then immediately restore it. There's more "space" to the right than to the left -- handy for illuminating the edge of the path if you ride on the right as we do.
The one small defect I found was the small rubber plug for the recharging port at the upper rear of the metal body of the light: the spindly little rubber strand linking the plug to its rubber loop-around-the-body gave out after a couple of years. I just replaced the plug with a 2 cm tab of plastic electrical tape, which in turn I replace every 2 or 3 years.
One related note of (in)convenience: The charging port on my light accepts a male tab on the USB cable which has a peculiar profile, unlike a common cellphone charging cord, for example -- the tab is thicker (taller), in the shape of a truncated triangle. A few years ago, I happened to find out that my Cygolite shares that with a Garmin eTrex 20, when the cable for the latter gave out.
If you should get a Cygolite, and if it has that oddly-shaped male tab on its charging cord, I'd suggest getting a spare -- in my limited experience with consumer electronics, I've seen only two devices with that profile.
Cheers, John