It has the extra buttons you get with eGo's "Extended Toolbar"http://wiki.beyondunreal.com/Extended_Toolbar
I am having a bit of a poke around it to see what is the same, and what is different (on the surface).
It defaults to save maps in Spatial Fear's format, but will happily open edit and and save UT maps.
I made a texture pack with it for a quick test, as I figure this will be one of the most standard import/export options.
No problems with that. Works fine in UT.
Then I edited an existing UT map, changed some textures, weapons, added some multi-texture windows, changed the physics on a few items, then re-rendered the lighting and saved.
Again works fine playing the map in UT.
I will obviously not be using it for my UT editing, unless I get more info on it's overall compatibility.
It installs into the UT system folder and shares UT and the editor's main files, but uses it's own config.