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I don't use his products, but Al Jacobs (Black Box) has been around for ages. Definitely not a "startup".
I do have a Cheetah lithium pack that can be used to power Nikon and Canon speedlights, although my use has been limited to their CL-180 flash. The battery pack comes with two power ports, and splitters are available for connecting up to 4 lights. Cheetah claims up to 1800 full-power pops with an SB-900. The lithium pack has worked flawlessly with the CL-180, but at $215 for the pack and $22 for the Nikon power cable, it's not the cheapest solution around. When it comes to SB-910's, I just keep spare AA's in my pocket.