You use a company with both the manufacturing capacity and the technical pipeline expertise. The advantages of this route are obvious and proven. When you have an organisation that can do both, you garner an intimate knowledge of the project and its pitfalls.
For example, having engineers on site to perform a line-stop and a flow re-route to remove the pipe burst, this will allow them to also to be on hand to install the fitting. You cut down on the number of organisations involved and remove the greatest chances of miscommunication.
By cutting down the number of organisations involved i.e. (a supplier and then a separate installation team), you will also be keeping costs as low as possible.
