Your first reference backs up my point that Muscarinic antagonism is a more favorable feature for the motor symptoms in Parkinson's disease than agonism (from your ref 'M1-selective antagonists may have weak antiparkinsonian activity but would not have the full efficacy observed in nonselective mAChR antagonists'). A273 has M1 to M4 agonism effect not antagonisms.
Your second ref is to an M1 positive allosteric modulator (strengthens agonism of the natural acetylcholine at M1). This could have pro-cognitive effect but I would expect little movement disorder effect
FWIW, I think A371 has more potential for PDD than A273.