The patch contains various bugfixes and game improvements such as widescreen support, and provides some GUI tweaks. It also enables the use of the FMSel fan mission loader frontend with Thief 3 and bundles the most important T3 mods. It works with the GOG and Steam versions of the game.
With the SU 1.1.9 Editor Edition, setting up an editor install for Thief 3 mapping is very easy. In the video, the Steam version of the game is used but it will work also with the GOG and original retail versions at least.