Very large PRODUCTS need a complete product management team to deliver the working product through multiple TEAMS, in this case, the product is divided into verticals which are being taken care of by different product owners. But if the product is small and can be delivered by smaller teams, a single product owner can suffice. In this case, the Product Owner will act as a single point of contact and can be the face of the client as compared to large products. 

Single product owner with smaller teams have a high rate of efficiency and delivery due to clarity in vision and goals, there is a lot of transparency among the scrum team and the stakeholders. In a few instances, the RPO MAY also act as team PO for one of the Scrum Teams with the help from other team Product owners on other delivery Teams. Having a product owner CATERS to multiple teams impacts the team functioning as they have to WAIT for the availability of the PO, along with this even the product owner has to ensure they are giving enough time to multiple teams.