I hope I'm not beating a dead horse here but what are your favorite tail lights? This time of year it's mainly gravel with a touch of pavement. I've been impressed with the output of my Planet Bike blinky light with the clear LED in the middle but their reliability has been a little disappointing. I am extremely paranoid about being seen (might have something to do with getting hit by a car this summer in the middle of the day!) I have been running approx 700 lumens in front.
I had a Planet Bike Superflash taillight break loose from it's outer mount and I had a switch that quit on another one To the mounts credit, when it broke I was on an extremely rough level b road on an unsuspended bike. I am currently running one like the light off Amazon on another bike and it's been good. It's really bright.
Although I no longer use them because I have brighter; I've used the PBSF before without any problems at all. I liked the first one so much I bought a second. I found all of the mounting hardware to be rock solid. When you slide the lamp into the mount there is an audible "click". That pretty much locks it in ( until you press on the plastic release just under the mount.
Also odd that you would have a malfunction with the light internals. While not the brightest of rear tail lights currently available, the PBSF set a new standard when it came out ( some years ago ). If you can find a better made light, buy it.
I'm another one who has had good luck with the PBSF. I still use one on the back of my camelpack. I ride enough though that I go through a lot of batteries (if the batteries aren't fresh the light is not near as bright) and I think I would be better served by a Surfas/Moonshield with rechargeable batteries (and brighter).
If I want SUPER BRIGHT I already have a light for that. Jim at Action-LED-Lights had some of his wide angle lenses made up in red and I've been using one with a Gemini Titan lighthead as a tail light. I even get compliments on the light from people in cars.
900 Chinese lumens makes a bright tail light! I actually run it on low (which is plenty bright) most of the time to minimize the decreased runtime I get on a battery charge (I use a y-cable). For me a self-contained light is a better fit since I seldom ride the same bike 2 days in a row (mounting take a little while), but if I were a commuter I'd use this light every time I went out. If you ride in traffic a lot and have an old MS/Gemini/Clone
lighthead, this is cheap way to make your ride safer!
Do not underestimate the importance of reflectors when sharing the road. Recently read something that the rear reflectors are seen before the blinking ones. My friends that commute also have replacing tape on their helmets and a small blindly facing the rear also.
I too use the Magicshine MJ818. I use a single battery pack to power the MJ818 tail light and either a MJ808U or MJ872 headlamp. I can't comment about how the MJ818 compares to other tail lights because I haven't used anything else, except an old school Vista Lite set to blinky mode for visibility, but the MJ818 sure is bright!