I'd read a few pop-sci articles about it, although this one provides the clearest description of the proposed drive; as I had surmised from the others, it's a pulsed-fusion drive, similar in concept to the Orion drive, although far less destructive of anything not immediately behind it.
Not sure why they're trying to reach break-even, as from the description they're using it for rocket-style thrust, not power, but perhaps I'm mistaken and they want to use a pulsed-fusion power plant to operate an ion drive (which could still make a Mars run inside 40 days, assuming Mars at opposition and an ion drive capable of generating about a hundredth of a gee constant thrust - say, if the VASIMR coupled-charge plasma thruster can be made to work at 200 kW for the required amount of time).
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Not sure why they're trying to reach break-even, as from the description they're using it for rocket-style thrust, not power, but perhaps I'm mistaken and they want to use a pulsed-fusion power plant to operate an ion drive (which could still make a Mars run inside 40 days, assuming Mars at opposition and an ion drive capable of generating about a hundredth of a gee constant thrust - say, if the VASIMR coupled-charge plasma thruster can be made to work at 200 kW for the required amount of time).