First I have not done anything beyond starting it up and looking around so i could be missing some things… plus of course I am steeped in the (API 1) Xojo way of doing things.
I can see that is there is a lot here and well done! It’s certainly capable of a lot… though does not have a number of the Xojo niceties (yet) that makes me more efficient, and coding less of a chore for me.
First there does not seem to me a property inspector for controls. One certainly can set them in code in the open event but for me the xojo way is more productive.
I use list boxes a lot in Xojo and very often they are hierarchical. It looks like Objo does not support hierarchical list boxes directly at this time… and if not, will it?
On listboxes in Xojo I tend to use Row and Cell Tags a lot… Particularly for hierarchical listboxes. I know that can be handled other ways but they are very convenient .
I also use the CellBackgoundPaint and CellTextPaint a lot in Xojo And I don’t see them in the list of events. That makes it possible to do a lot of in the Xojo Listbox that would not be possible otherwise.
On Listbox sorting I think the Xojo CompareRows is nicer than handling everything in header pressed and custom sorting… Less work and more approachable for someone new to coding IMO.
BTW besides sorting, in xojo I sometime use the CompareRows event to freeze one or more rows at the top when sorting and it is quick and easy to do that.
I won’t ask for the Objo listbox to support merging cells across rows and columns! 
- Karen