What is FollowMainForm in TFormSize used for?

I have a TFormSize that I'm using on additional dialogs that popup. I didn't want to save the position, just the size because I want it to come up centered over parent. The problem is that the centering is done prior to TFormSize adjusting the size so it's not centered in the parent window. I thought maybe that other option would help (at this point I was saving position too) but when I moved the main window and opened again, it just stayed where it was.

I think TFormSize should look at the dialog to see if Position is poMainFormCenter and if so, after changing the size, centering it if position is not being saved.

Does it help when you set Form.Position again to poMainFormCenter from the FormSize.OnLoaded event?

I don't see that event available - all I have under events is "DataSource" and "OnError"

Also what exactly is "FollowMainForm" and "Magnet" mean/do?

When you move it to the edge of the screen, it sticks to the screen edge

Please use the latest version v1.5.0.0

How do I know what version I'm using? I have the registered version.

I get "Project myapp.exe raised exception class EInvalidOperation with message 'Cannot change Visible in OnShow or OnHide'.

The component version is in the object inspector.
The TMS VCL UI Pack latest version is v12.1.0.1
You can always check the latest version of TMS VCL UI Pack at: TMS VCL UI Pack Our bundle of over 600 VCL UI controls for modern, feature-rich Windows application development, including grids, planner, richeditor, ribbon, web updater, treeview and much more...