The main idea of this article is to identify the benefits of the full vehicle substitution process for a fully sustainable Urban Freight Transport (UFT) in economic, social, and environmental terms, based on the application of the experimental method. The scientific assumption was made that Electric Delivery Vehicles (EFV) can be complementary in the first stage, and only in the next stage, substitutable to the traditional diesel-powered fleet servicing transport (courier) tasks within the delivery limits in the Szczecin Agglomeration. To assess the level of substitutability, observational instruments were used, while ensuring an active modification of the studied phenomenon (introduction to the operation of selected routes of electric vehicles). The focus was on three key elements, the environment, rules, and regularities. The article presents the architecture of such experiments regarding 22 selected routes, which allowed for the calculation of selected performance indicators for ex-ante evaluation in planning delivery scenarios. The results were verified using a simulation-based approach in the Szczecin Metropolitan Area. As a result, it made it possible to find answers to the research questions posed, in particular: is it possible to fully replace combustion-engine vans with electric ones, and what integrated benefits can be identified, and their systematics has been illustrated in the proposed proprietary model “Electromobility Octagon Profit”. Future research could extend the theoretical knowledge by further exploring the development processes for the use of electric vehicles in the urban freight transport system and by adding insights from other contexts, stakeholders, and theoretical areas.