The write-up that "rm -rf" did on the Hotshot 150 was very well done. I've been using the same rear light for the last year or so and I've been very pleased with how it works. Not to mention that for what you are getting it is very affordable. If your goal is to be seen from behind at a distance the 150 gets it done. I don't use mine during the day but I suppose if I did I would switch it from the " fade in / out " mode I usually use to one of the sharper, "Flash/pulse" modes.

Like Mr. RM said the Hotshot is only going to work for group rides on the steady mode which you can adjust down to a bare minimum output. Otherwise for group rides I suggest buying a cheaper / lower output rear blinkie, one that also offers a lower output flash mode if you think you might want that. Sometimes you can buy these for less than $15. Last year I bought one of these cheap Blitzu Gator set-ups just to screw around with. Turns out it came with a nice little rear light that has 3 intensity modes for flash and three for steady. Low flash or low steady with this little Blitzu light would serve you very well on group rides. Too bad they don't seem to sell these little rear lights separately. If they did they would likely sell for around $10.