As you already know, the incompatibility of the Cydia application with iOS 4.2.1 was one of the main reasons why the jailbreak solution for iOS 4.2.1 was a little difficult. The new version of the Cydia application, which has been worked on for some time, does not bring major changes for iPhone/iPod Touch owners from an aesthetic point of view, the only differences you will notice will be the buttons at the top and the one in stopping the update. With the iPad tablet, the situation is different because Cydia is now compatible with the tablet, it also allows working in landscape mode, so iPad tablet owners are the most pampered.
From the performance point of view, I have to admit that the new version of Cydia is a bit faster in loading information/installing applications, so overall you will notice an increase in performance. Unfortunately, from a graphical point of view, the situation is still not 100% ok because when switching between menus, you will notice that the graphics go a little crazy until all the information is loaded, then everything returns to normal.
At the moment cydia_1.0.3366-1 is the public version from redsn0w 0.9.6 beta 4 which you can also install on iOS 4.1 using the tutorial this or this. But first you have to download the new version of Cydia from here. This version may cause problems for some iPod Touch 2G owners, I don't know about the other terminals, so be careful.
Version 1.0.3366-7 of Cydia is being tested and will be published soon, and I recommend you to wait for it because it seems to work a bit better than the previous one.
