merging faces to a single surface

Hello,

I created a screw-shell using BRepOffsetAPI_ThruSections with several rotated faces as sections. This worked out fine apart from the long time it takes to compute. However, as a result I do not get a single shell surface, but a compound of several faces (see attached image).

What function can I use to merge these to a single (sur)face?
From what I found in OCCT Documentation, there are two optinons:
1) ShapeUpgrade_UnifySameDomain Class and
2) TopExp_Explorer to get the faces from the shell that results from BRepOffsetAPI_ThruSections combined with BRepAlgoAPI_Fuse to fuse the faces

What is the right way to do this?

Thanks in advance for your help!