Inexpensive
Platform  specific, for example testing on Oracle it’s less than 1% of one cpu

Fast
Sample every second, refresh every 5 seconds

Powerful
Sample once a second user states and build up a model of load on database.
We collect multiple attributes about the active users and the data can be aggregated in different dimensions. We display different dimensions such as top SQL, Event, Session on the database or for a specific session the sessions top sql, the sessions top event, or for a SQL statement the top sessions executing that SQL, the top wait events for the SQL or for an event the top sessions running into that event and the top sql running into that event.

Small but concentrated
Amount of data depends on the number or active sessions. More active sessions, more data. Less active sessions less data. Typically data is small for example less than 1M for an hour of profiling for 10 active sessions.

Eclipse, saves the icon layout incase it’s customized and reuses that layout, thus if the load editor wasn’t there it won’t be  shown. The easiest way to make it appear is just to use a different workspace.  The workspace is prompted for at startup or it can be changed with the menu
                File->Switch Workspace->Other…
and/or
                Window -> Reset Perspective

If connecting with TNS change to direct connection and test. When connecting with TNS and using a client driver that is inferior to the monitored database some of the queries don't work properly. You can also check what Oracle version you are using running (which.exe is a link to a downloadable executable for windows)
         which.exe tnsping.exe
The executing that command with full path.