[TigersEye]

What is a tiny bit of wear going to do to the fit?

They address that in two ways it appears.

There are no angular forces pushing the piston against the cylinder walls eliminating the frictional losses of crankshaft engines. The compression/combustion forces are directly in line with the piston/cylinder centerlines. (See illustration “A”)

In the CC Engine there is clearance between the cylinder wall and the piston to allow for any thermal changes and component wear, there is no lubrication needed on the cylinder walls. The piston-cylinder pressure seal is in a cartridge located at the entry of the cylinder and allowed to float within the limits of piston-cylinder clearance.

[Revel]

They have a picture of those rings in the images section.

[count-your-change]

That sounds good but that cylinder has to hit the the mark with virtually perfect alignment despite gear wear and manufacturing tolerances.

A handmade model or one in a video simulation is fine but other than a novel design it's hard to see any advantage over a cam engine or multivalve conventional engine.