I must be stupid or there's really no information anywere to be found about what the Redux version changes.
So, what's the difference between the normal and the redux version?

I must agree! Trying to figure out what this Redux version has the original doesn't, and why it suddenly showed up in my library.

With the Redux version, Ether One runs now on Unreal Engine 4 (instead of UE 3), which means that the game optimization is way better and get some visual improvements as well.

As stardust_79 said Ether One was completely rebuilt in UE4 which means that it will probably run better on newer systems than the original game. There are visual enhancements as well as added animations and sound effects. The devs also added additional translations (subtitles) for the game. I did the German translation myself and was able to test the game multiple times while it was in beta state. I also did some comparision screenshots which I will add in a moment. The game itself has not changed - still the same puzzles and solutions and still the same great story. The devs have worked on this for over a year and they give it away for free to every owner of Ether One so if you buy it you will receive both versions.

Edit: Here are the screenshots (first normal, second redux, third normal ...):

http://markoh01.lima-city.de/Ether%20One/01.jpg
http://markoh01.lima-city.de/Ether%20One/02.jpg
http://markoh01.lima-city.de/Ether%20One/03.jpg
http://markoh01.lima-city.de/Ether%20One/04.jpg
http://markoh01.lima-city.de/Ether%20One/05.jpg
http://markoh01.lima-city.de/Ether%20One/06.jpg
http://markoh01.lima-city.de/Ether%20One/07.jpg
http://markoh01.lima-city.de/Ether%20One/08.jpg
http://markoh01.lima-city.de/Ether%20One/09.jpg
http://markoh01.lima-city.de/Ether%20One/10.jpg
http://markoh01.lima-city.de/Ether%20One/11.jpg
http://markoh01.lima-city.de/Ether%20One/12.jpg
http://markoh01.lima-city.de/Ether%20One/13.jpg
http://markoh01.lima-city.de/Ether%20One/14.jpg
http://markoh01.lima-city.de/Ether%20One/15.jpg
http://markoh01.lima-city.de/Ether%20One/16.jpg
http://markoh01.lima-city.de/Ether%20One/17.jpg
http://markoh01.lima-city.de/Ether%20One/18.jpg
http://markoh01.lima-city.de/Ether%20One/19.jpg
http://markoh01.lima-city.de/Ether%20One/20.jpg
http://markoh01.lima-city.de/Ether%20One/21.jpg
http://markoh01.lima-city.de/Ether%20One/22.jpg
http://markoh01.lima-city.de/Ether%20One/23.jpg
http://markoh01.lima-city.de/Ether%20One/24.jpg
http://markoh01.lima-city.de/Ether%20One/25.jpg
http://markoh01.lima-city.de/Ether%20One/26.jpg
http://markoh01.lima-city.de/Ether%20One/27.jpg
http://markoh01.lima-city.de/Ether%20One/28.jpg
http://markoh01.lima-city.de/Ether%20One/29.jpg
http://markoh01.lima-city.de/Ether%20One/30.jpg
http://markoh01.lima-city.de/Ether%20One/31.jpg
http://markoh01.lima-city.de/Ether%20One/32.jpg
http://markoh01.lima-city.de/Ether%20One/33.jpg
http://markoh01.lima-city.de/Ether%20One/34.jpg
http://markoh01.lima-city.de/Ether%20One/35.jpg
http://markoh01.lima-city.de/Ether%20One/36.jpg

A quick remark to thoose of you who are using the German translation:
In the game there are several blackboards as well as signs. Some of the important ones you can read by holding the left mouse button (normally it displays a description of the object but in this case it will show the translation) and some of them will be translated by double clicking on them. However a few signs are only be translated when you readi them in the case (you can teleport there anytime) where you can find them on a board down the stairs. I worked for months on the translation and tried to make it as professional as possible. It's also important that you adjust the settings in the game options menu to reflect your keyboard layout. Otherwise some special keys (like ":") which you'll need to solve some of the puzzles won't work correctly if you don't use an English keyboard, If you have any additional questions regarding the redux version and especially the German translation feel free to ask.

Thanks for the information and the comparison screenshots!
+1 =)

Yeah thanks for the explanation and those shots. It appears it will be worth another download, as I haven't yet started the game.