If I can rant for a moment about modern watchmakers(please pardon me, as it really is a great watch) I don't know where this idiotic "deadbeat" term came from.
In horology, "dead beat" has always referred to a type of escapement, most generally a clock escapement where the pendulum only receives an impulse in one direction(i.e. it has a "dead beat" in every cycle).
Since the beginning of time, mechanical watches which advanced the second in "jumps" rather than with each oscillation of the escapement has been called a "jump second."
In the past, one way to get a jump second was to use a so called "Chinese Duplex" escapement(for its popularity in the Chinese market) which had a quarter-deadbeat duplex escapement running at 14,400 bph, giving one "jump" per second.
In any case, please pardon my rant. I love JLC and that's a great looking watch-I just wish that they wouldn't feel the need to invent or mis-apply terminology.
Well, they called it a "True Second" so I guess I'm mistaken when I called it a "Dead beat." All I know is that the Caliber 770 that's in the Geophysic True Second stores the energy in the escapement and releases it once per second so the second hand only moves once per second.
http://www.ablogtowatch.com/jaeger-lecoultre-geophysic-true-second-watch-new-movement/
https://www.hodinkee.com/articles/the-jaeger-lecoultre-geophysic-true-second
Anyway, I feel like the JLC Geophysic True Second is very interesting considering all current production iterations of a "dead beat" second have an even higher price point.