If we were serious about CO2 capture, then the place to start would be big producers (like coal plants): Because that way you need much less scrubbing efficiency and can tolerate much greater overhead while still being effective.

If a technology is not good enough for at least serious trials in that (much simpler and more forgiving) usecase, then there is no point in discussing it for small environmental air scrubbing. That is akin to talking about electrifying passenger planes before having a single electric vehicle on roads.