We bought it together with the cover bar just in case we needed it. The frontcover works really well. After our second cat kept forcing the feedee open we just gave him access.
Once that happened, our third cat started putting his head in the feeder while the other was eating. She did not do that before, probably because she still hates our new adopted cat.
However, after installing the front cover, our third cat can no longer steal food. This is really helpful since she will eat anything she sees until she pukes, while our other cats stopt when they have eaten enough.