Is there a risk of metal-ceramic layer growing in excess? Can it cause the engine to seize up? 

No an XADO will not damage your engine. XADO revitalizants are completely soluble in the oil and do not change the viscosity of the properties of the oil in any way. Remember XADO is self-regulating. As soon as the original worn surface has been repaired, the friction factor drops dramatically, and the XADO activation energy will also decrease. The process then stabilizes, and at some point, the energy will drop to a point where cermet growth will stop completely. Besides, using too much is just a waste of money.