However, while that article says they will not be able to be a collective bargaining unit under US law with that structure, the announcement oped in the NY Times (https://www.nytimes.com/2021/01/04/opinion/google-union.html) implies they will be pursuing becoming one, so not sure if that nontraditional structure is temporary or if the Post got some details wrong.
There is a great line of research that part of labor's downfall in the postwar era was due to becoming to legalized/instituionalized, creating a hysteresis trap were the unions official power (laws and norms) lagged behind the underlying conditions that give it real power (labor scarcity + worker radicalization). Workers got complacent and depoliticized starting with the red scare, and edges along by shitty union leadership, and the whole Regan era turnabout was less a right-wing conspiracy and more the hysteresis delay coming to an an end.
Members-only unions and whatnot that forgo the NRLB are "riskier" in some sense, but that vary precarity / forgoing of intertia can avoid the lag and help keep the union vigilant.
I understand AWU is currently following the CWA "Solidarity Union" model: not currently seeking recognition but may choose to do so in the future.
(Disclosure: I am a member of AWU)