This rating only applies to Vienna3.1.4, which finally got it right.
I've been using this app for a few years now and I have to say, up until this latest version, it has been the buggiest, most unresponsive app I have ever used. The only reason I stuck with it is that there is nothing else that even comes close to its (poorly implemented) functionality. That said, previous versions were impossible to navigate with just the keyboard because the app refreshed the display of every feed as you went up/down the list, even though the content itself was not refreshed. It took ages to get from one feed to a target feed so I was forced to use the track pad, something I try to avoid. Much to my disbelief, this behavior has been eliminated in the new version! Thank you! Another thing was the unresponsiveness in general. First it took many minutes for the app to start up and stabilize. Then manually refreshing all feeds took many more minutes. Next, I caught the app hogging 100% of one CPU while it idled, even though I had settings to manually refresh feeds! If it quit at all, using the normal Quit mechanism, it would take many more minutes to finally quit. Oftentimes I had to force quit it because it became unresponsive during the quit cycle! Another really annoying thing was that, if I left the app idle for any period of time, and then tried to go back to it, it was unresponsive and I had no choice but to force quit it. Force quitting an app is not something you want to do ever, but especially not on a regular basis.
I just started using 3.1.4. It started up very swiftly and refreshing all feeds was much faster. I can navigate the side panel with the up/down cursor keys very quickly, without any lag. I can quit the app instantly now and restart it instantly. It is using practically no CPU cycles during idle times. This is the first version that works as I always hoped it would work. That's great news to me. There are still some quirks with the UI that need to be changed, but that's another version…