...I believe you're mistaken.
The Lange Double Split is, although exceptional in the regard that it is a double rattrapante, still a normal split chronograph.
I.e. by pushing the split second button, the running chronograph time is "freezed", can be read and taken record of etc.
The difference from a normal split second is, this applies to the chronograph minute register hand as well.
If the split second button is pressed again, both hands will synchronize with the chronograph hands. That's it, impressive, but
still a normal rattrapante (although extended to the chronograph minute counter).
Practically this means, with a normal split second , one has to be aware, that care has to be taken with time reading, i.e. the respective minutes of
chronograph time. This is more comfortable with a double split, as you can take more time to record the split time, minutes are split as well.
Is it worth the plus in complexity? That's more or less a matter of taste - technically I doubt it's really helpfull - but that's my humble oppinion only.
Re. the described PP caliber - IMO a typical PP approach - the right mix of complication, paired with lot's of technical elegance (very flat for this combo) and
some "modern" aspects as well (altered beat rate as well as some mechanical solutions in the chrono...). For my taste, they could have left out
some of the "modern" aspects and kept it a bit more traditional - but again that's me.
I like the overall look quite a lot - especially the basic dial layout/choice of guichet indications - the hour/minute hands as well as the hour index design
isn't for me though (what the h*** had the designer in mind )
BTW, who else tinks the PP seal is a bit , hmmmm, am I allowed to say ugly ??
Too large, bold and....please, just for the looks, give us back the nice, discrete Geneva seal
Best regards
Suitbert