Using Transaction Groups for PLC Sync

While I would normally use produced consumed tags to share data between PLCs, I have a situation where I cannot modify the I/O for a controller and need to synchronize data through another means.

While I know that TGs are normally used in the context of transferring data to and from the OPC and databases, in the ignition documentation it mention syncing PLCs as a typical TG use:

Sync PLCs - Items in the group can be set to target other items, both for one-way and bidirectional syncing. By adding items from multiple PLCs to the group, you can set the items of one PLC to sync with the others. By creating expression items that map from one PLC item to the other, you can manipulate the value before passing it on.

I would like to try this out, but need some guidance. I’ve created one set of OPC tags as ‘Read Only’ on a target PLC, and then another equivalent set from the source PLC with a ‘Write Target’ between corresponding tags.

If I want to make this bidirectional, I’ll need to create another transaction group, correct?

What should the update mode be set to, to ensure that there is no database query? Or does this not matter?

This is what I came up with. I’m still unsure if the update mode is correct.