The plug-in is basically marketed toward people who desire (or in your case, are forced) to work within the Eclipse environment and want to use the SlickEdit editor...or just want a much more powerful/flexible editor than is provided by any Eclipse plug-in.
It is the exact same SlickEdit editor you are used to, just plugged right into Eclipse. All the language support features are there. We try not to duplicate functionality within Eclipse when it's not necessary. For example, there is no reason for us to expose SlickEdit's version control support because we feel that Eclipse handles version control very well. We have included our diff tool because we feel it offers features above and beyond the Eclipse diff tool.
There are some features which are specific to the plug-in and not in the normal SlickEdit product, but they are mostly to better integrate us into the Eclipse environment. For example, we have an overview ruler to the right of the editor in our Eclipse plug-in, and this feature (which is great) does not exist in normal SlickEdit. We implemented it for our Eclipse editor because Eclipse users are not used to working without this feature (shows you a full file view of all bookmarks/errors/warnings/tasks/etc. in the current file).
I hope this helped to clear up how the plug-in differs from our standalone product...and I recommend you check out a trial to see if it will work for you. Just know that the latest version of the plug-in does not run in a 64bit JVM, and therefore will not run in 64bit Eclipse...this is the most common setup/installation problem.
- Ryan