In a densely occupied room (if that will continue to exist), it may thus be difficult to detect an effect of air cleaning far from the unit. Furthermore, poorly designed units may add ozone to the air, which is indeed an unwanted side effect.
Both REHVA and ASHRAE quickly established working groups that in little time have worked intensly to elaborate practical guidelines for appropriate building operation in the wake of the pandemic. Naturally, the guidelines overlap to some degree, but they both emphasize that recommendations are targeted specialists with at least a minimum knowledge of ventilation and air distribution. Some background knowledge is thus required to evaluate if use of a technology or initiative is meaningful in a given situation.
It is unfortunate if marketing of technical solutions to reduce disease transmission is not trustworthy. This can be caused by the vendor's lack of knowledge or a wish to make a fast profit. This may have negative, budgetary side effects, e.g. in schools with limited budgets who need to act, but do not possess the required technical knowledge to evaluate the performance in practice of a solution. As building professionals with expertise in ventilation, we have a responsibility to assess, articulate and give advice on efficient solutions and maybe even more on those that are not efficient.