This does even less for me than iMCPEdit. I can change the game mode with iMCPEdit although when I do it sends me to x:0 y:0 z:0 and all other values including items are at zero.It still has a bright future though.
Make sure you're typing the entire URL into Cydia's sources.
On a side note, I am working on this again. I will try to push out new builds by the end of the week (at the very least, replace the icon because plain white is awful). I am not sure why Cydia says the app is always needing an update, I will try to fix that (I probably wrote some file incorrectly).