I test dove the Sola 4000 in the Channel Islands yesterday (courtesy of Blue Water Photo) and mounted it on the center post on my L&M Stingray housing (I have two ULCS arms on the handles, each carrying a Big Blue VL1300 light). I was mainly practicing macro and for this purpose they are definitely too bright at full power. Essentially, I was using position 4 or less (out of 7), otherwise I could see the Sony CX500V adjusting the gain downwards. I tried a few "wide angle" shots and the light did not make any apparent difference in terms of water penetration with full power. In fact, when turning my two BB lights (supposedly 2,600 lumens total) and the Sola (supposedly 4,000 lumens), I did not feel like there was a major boost in illumination power... But then again, this is SoCal and the viz is not always that great (although we had easily 30+ ft of viz during that trip).
I did not keep the lights on permanently, but right during the first dive, the red LEDs in the back turned on (supposedly telling me that the battery was getting low). The light was brand new and had been charged the night before, so I and BWP were quite surprised.
Anyhow I went ahead with three more dives without any surface interval recharging (1 hr each, I probably could have tried that). Early on during the last dive, the light shut itself off. Meanwhile, my BB VL1300 were still burning strong and were more than enough for all my shots (again macro, so not too demanding). I think I remember it did turn off a couple times in previous dives, but at least I could turn the light back on. This time, it was the end.
In summary, I was not blown away by the light, although I probably did not use them in the most appropriate conditions. Moreover, considering that you need two of these to set up the proper light in macro (or for any kind of shot as a matter of fact), that's an investment that deserve serious testing. In my case, the 2 BB lights cost me less than the price of the Sola (from my estimation, the lumen/dollar is about the same for both products. Note that the BB lights are not represented in L&M comparison chart)
I am grateful to BWP for having given me the opportunity to test the light and would be happy to hear different feedback on the light.
PS: I'll not that the new Sola 2000 could potentially be interesting too, but since they L&M claims similar burn times as for the 4000, I have some doubts about the practical relevance of these figures...