It depends a bit on what your client wants to be able to do:
- Simple consultation to validate the design, an export/import in step/iges/parasolid or even an executable edrawing will be very good
- get the design back to possibly make modifications, it's going to go badly because he'll lose the construction tree, the relationships between the parts, etc.
Sorry for my late intervention, I hope that since that time you have been able to find a solution to your problems.
That being said, according to software merchants, there would be no problem to go from SE to SW and vice versaille. In practice, it also depends on the versions used, in any case, there is a good chance that the tree structure will be lost and the assembly links will be incompatible.
As an OS user, I retrieve the "parts" under step files and I recreate the assemblies. With subcontractors, I also had the opportunity to use the sending of 3D Pdf files, very practical for quick view-ups and other notations.