The prefabricated outlet was initially introduced to make things easier and swifter for DIY customers.
Regular installers of the Infinity Galvanized steel (copper and zinc) rainwater system were accustomed to cutting out a hole in the gutter anywhere along the gutter length that they required a drop to a downpipe.
The brief video instructions for gutting and prepping the hole in a gutter length for the wrap-around outlet can be found here: https://youtu.be/f55JHPnO_xo
Download the wrap-around outlet gutter cutting guide here: https://www.rainclearsystems.co.uk/steel-wrap-around-outlet-gutter-cutting-guidance
By contrast the prefab outlet comes with the hole, pre-cut in a 300mm gutter length and the outlet already wrapped around it.
Really it is entirely up to you to choose which one suits your needs best in any gutter run, in any project. Having to two options just gives you more choice.
Just remember to order two gutter unions for each prefab outlet (unless it sits perfectly at the very end of the gutter run).
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