The Walk Through Walls keybind has been renamed "Time to Fly" and now works much, much better along the Y axis. I recommend a WTW Camera Y Correction of 3. The original Time to Fly keybind has been deprecated.
The "Down/Up" slider on the GUI, in combination with the "Freeze Y" checkbox, will now allow you to run around in the air as if you were standing on solid ground. The Movement Speed Hack must be enabled.
The Create Solid Ground keybind essentially prevents falling and allows for running around in the air. The Movement Speed Hack must be enabled.
These improvements require updating Speeder to version 55.