I'm planning a 10x10 tent, so if I go with BML I'd get (6) Spydr 600s, 3 along one wall and 3 along the opposite wall. That way there's room in the middle to move around, and somewhere to put a reservoir, etc... I realize most people just stuff the whole tent and access it from the sides, but this is a pretty big tent, and I like to be comfortable while gardening.
My concern with BML is that they're not enough watts for the area they cover. However, they do show it covering a 4x4 area in the video and say it's stupidly efficient. The nug results of the one BML grow thread that exists do look high quality, even if the yield wasn't massive. Each Spydr 600 weighs 23 lbs, so 6 of them would be a lot lighter than 4 AT600, which are 60 lbs each.
If I go with Area 51 I'd have to stack them two deep, and then it might be a pain to adjust the ones in the back... so you've almost got me sold on these. Thing is, I don't really have time to do a whole grow under one before deciding on more, and since they're not proven, it would be kind of a big gamble. They are designed for greenhouses after all. But still, I might do it.
The other fanless option is Illumitex, which are even more expensive, right? Another thought is, I could hang some 70 watt vertical induction bulbs between the Spydrs.