I finally took this light (EDI-T from the OP) in the water. I took it and an Xtar D26 and compared the beams side by side. I was at around 60' in my local quarry, so it was both dark and low viz.
The EDI-T definitely has a bigger spot. The spot seems to be not quite as bright as the spot of the D26, but I guess that shouldn't be a huge surprise. It might be more lumens, but if you spread them out enough, they're not going to illuminate any one thing as well.
So, it's a tradeoff. Bigger spot or brighter spot? I guess they both have their place. But, the EDI-T spot is not THAT much bigger....
For me, the physical size of the EDI-T really puts me off. The head is WAY bigger than the D26 (or a DGX 600), and the body is a noticeable amount longer.
I also did not especially like the twist-ring of the EDI-T. It seemed to accidentally turn on too easily. This has something to do, I know, with how I carry it, which is clipped to a chest D-ring and then tucking the head end into an elastic loop on my shoulder strap.
I think I might opt to use the EDI-T for night dives (maybe), but will stick with the D26 for anything else. The EDI-T is a maybe for night dives mainly because I have an Archon D11V which has a 70 degree beam angle. But, it's only 1 LED emitter (claimed 860 lumens), so it would be a fair bit less bright. However, at night, it might still be bright enough. I'll have to compare them, at some point.
At this point, I'm feeling like any light that has more than 1 LED emitter or carries more than 1 battery should (for me) be a can light. If it needs more than 1 LED, the head will be big enough that I don't want the needed battery can attached directly to the back. That makes it too unwieldy for putting in a soft Goodman handle on the back of my hand. And if it has more than 1 battery in it*, the body will be too long and, again, too unwieldy for hand mounting. Either way, the batteries should just be in a can on my belt.
And I currently have no need for something brighter than a 1 LED light or that burns longer than 1 LED with 1 good battery. So, no can light for me (yet). I just don't see needing a can light until such time as I were to start doing cave diving and get to the point of doing long ones.
* an exception would be any light, like the Xtar D35, that has multiple batteries all side by side, instead of end to end. The D35 has 3 x 18650 batteries, but it's not any longer than a single cell light because the batteries are all side by side in the handle. Unfortunately, the light head on that one is 3 LEDs and, I think, too big, just like the EDI-T light head. And the D35 is too dang expensive! $200 for a light that is almost the same as the $22 EDI-T light?!?! Crazy!
