Originally Posted by 2manybikes
The Cateye is less money. It may be a little brighter directly from directly behind. But it loses a lot more when viewed off axis (say 45 degrees off of straight behind.)
The Nightrider may be better when you are surrounded by heavy traffic and you need maximum visibility from all angles. If your riding on rural roads and the cars can see you a long way off the Cateye is good too.
I wound up buying both. The NR wasn't in stock and I didn't want to ride a few days with no rear light so I bought the other as a backup. I must say I'm impressed. Had I seen this a few years back, I never would have even thought to look at the NR.
However, I ordered the NR anyway and I plan to run both so I always have a backup. Lights are no place to economize.
To the OP -- the Blackburn Mars 2.0 was also in my LBS. It's a decent light and is much better than most small blinkies.