I've been using 2 x 600s since Oct last year. I use them primarily as a video light source.
I use them 5/6 times a week, two dives a day. I switch them on and off constantly, they generally reach their low battery at the end of the two dives and then I charge them every day. I don't use the red setting.
I've found that the switch sticks randomly. This isn't a massive problem as I'm now used to sliding the switch with my fingers and pulling it back to the neutral position, before that I'd flick it, it would stick and then turn the light off.
I've found that the time it takes to turn the lights off is a bit annoying, it takes too long, especially when you have two!
One light has only ever failed to come on once, then I switched it off and a couple of minutes later switching it back on it worked fine (this is after hundreds of dives so I wouldn't even consider it.)
The connections are corroding ever so slightly (something I can clean up), but apart from that the units have little signs of use.
Under use one of the lights is starting to move from the fully charged, green, state to the orange state a lot quicker than the other one and when I plug it in to charge after the day's dives it goes straight to green. I've raised it with L&M who have said if I can try get it back to the supplier they'll replace it for me.
Overall, their form factor is incredible, the light (for video) is great, I rarely take it off the first setting. I used it a couple of times on a night dive and the red really does work. On a dive with plenty of worm action I had one on the white light and one on the red and there must have been 1/10th of the worms in front of the red light.
I wouldn't say that the fish were completely unaware of the red light, they scared slightly less with the red over the white, but they still knew about me.
For a focus light, the only thing I'd say, with mine, is that the red light doesn't have the coverage required for a focus point for WA, it significantly drops off after a couple of feet, but I couldn't see that being a problem really.
No fear of flooding, stick them in your pocket, ideal for traveling and also very bright!