[mrcommentwriter]

Interesting, I haven’t heard of anyone doing this before. What is the advantage?

Assuming 120v loads are split reasonably equally between each leg of the 240v phase, the load will mostly be on the 240v circuit because both legs are connected in series. The neutral back to the transformer is only used to carry the difference between the 120v load on each leg of the phase, and also to keep the system grounded.

I guess if you had a panel close to load capacity, as well as a single very high amp 120v device, the transformer could enable some more capacity by ensuring the load was distributed equally between the phases. However at that point a service upgrade would probably be necessary anyway based on the load calculation rules in the code. Also high amp 120v devices are quite rare as far as I know, so I was wondering why you went with this unusual setup.