Is the "Update Main Translation Memory" task actully running an import of the SDLXLIFF file in the background? Is there any difference between updating TMs from within a project and importing the same SDLXLIFF file into the same TM?

This is the background:

We have a number of Studio projects and we would want to import their contents into a new empty translation memory. Both the projects and the translation memory have a text field to identify the document being translated.

As far as I can see, I have two ways of achieving this using the API and mirroring what a user would do manually:

A) Update Main TMs.

1. Open each project, change in the project settings and add my new TM to the list of  translation memories. 

2. Run the Update Main TMs task. The Update task will use the value of the Text 

3. Close the project.

B) Importing the SDLXLIF files

1. Open the new TM.

2. Run one import for each SDLXLIFF file (each should have a different value in the text field).

I have to look into which option would be more straightforward and the SDK contains samples for both approaches.

My question, however, is if the resulting TM would be different in anyway depending on whether I use one procedure or the other. The available options are the same in both cases and I have the impression that the "Update Main TMs" task is in reality running and import in the background but I have not found any description anywhere.

Daniel