Just tested this and it's kinda cool! The only thing I think it is missing is a "REMOVE BOXCAM" button that would remove the expression(s) from selected layers.
could it be that this script does not work anymore in the cc 2018 v 16.0 update ?
The CC 2019 update (v16) introduced a new ExtendScript engine, which could've broken Boxcam I'll investigate and try to issue a hotfix, but for now you can make it use the legacy version by going to File > Project Settings > Expressions and selecting the "Legacy ExtendScript" option
I'll investigate and try to issue a hotfix, but for now you can make it use the legacy version by going to File > Project Settings > Expressions and selecting the "Legacy ExtendScript" option