A three-zone anteroom really eases the order of biosecurity practices in the hygiene lock to reduce contamination risk : (1) removing shoes and coat, (2) then wash hands, (3) then put farm/barn specific shoes and clothes. It also better separates the zones.
In fact, it may require as little as an extrabench or planck in the hygiene lock (and so little space as a meter-wide intermediate zone). Did you ever try to install this system or advise it to a farmer? Some super small hygiene locks may not be adapted but I believe that many are.
