Check the following points

1. If you are using 2 screens, DPP must be in the main screen else DPP++ extensions will not appear.
2. In the preferences menu of DPP, put the tool palette in docking mode else DPP++ extensions will not appear.
3. Use the edit image window to edit your images else DPP++ extensions will not appear (when you are in the main window, select your pics and then use CTRL + –> )
4. Clic on the program icon in the notification area (bottom right of the screen).

DPP++ extensions appear only when DPP or DPP++ are the active windows (windows that have the focus). For instance if you put DPP's window besides NotePad's window, and if you clic on the notepad window, then the notepad window becomes active and DPP++ extensions disappear. But if you clic on DPP's window then DPP becomes the active window and DPP++ extension should appear. When you clic on the DPP++'s program icon in the notification area, in this case the DPP++'s window is active and the extensions should also appear.

If you open a folder with several images in the main window, you have to wait until DPP finishes drawing all the thumbnails before going to the edit image window. Else DPP continues to draw the thumbnails in the background and this is the thing that creates the mouse freezes. So, when you are in the main window, just wait until DPP finishes drawing ALL the thumbnails before start editing in the edit image window.

Custom picture styles are managed in a different way in DPP than standard ones. There is a technical problem to load them through a plugin program. However since version 5.1 a solution to this problem seems to be possible. Please keep an eye on next versions.

As new versions are posted frequently, you don't need to acquire each new update. Some updates are minors, others are majors (new functions introduced). You may just wait for a major new version before updating.