This is the first time I've seen or heard of the the pivotal-piston, but seeing the website-illustrations has my mind reeling.
Motion is stablized, but surface-area is greatly-increased and as you inferred it would seem possibly- more-difficult to contain the combustion gasses.
Then, I get into all the different ways the top-connecting-point of the connecting-rod, might travel-horizontally along the horizontal, and all the different ways that might be used to adjust the Torque/Power curves (possibly on the fly) and I really start going NUTS.
Anyway, if they ever get it to work it'll be cool, but right now I have my doubts...and a Hellava-Head-Ache!