Hi,
Bringing than one more supplier is indeed more than necesseray but can be challenging for the client :
- He will need to esablish clear specifications : depending on his business this is something he might not be able to do easily, especially if he worked for one same suppliers who know its business for years
- He needs to look for alternative and reliable suppliers : depending on the business could be not that common and in the end risky
The additonal reasons (on top of what you mentionned already) why it's important not to be too much exposed to one unique supplier :
- risk management : in case of supplier failure, breakdown, conflict. Make sure you have an alternative
- cost reduction : even though the relation is excellent, always good to create a comptetion to optimize your cost
Hope this helps
Benjamin