I know this is subjective, but it's so hard to find a good rss reader with a modern UI and isn't inexpensive/free
There's a Reeder 5 and the two improvements (for me) that it has over 3 is that Twitter probably won't say "outdated browser" and refuse to show tweets and support for adding newsfeeds directly. I think MacOS added support for this after Reeder 3 was released.
Mixing the two readers is fine because Feedly is keeping track for them. If Feedly were to start charging, I'd probably start using NNW exclusively since they provide the option of using iCloud to sync.
To me RSS and the reader are and should be separate.
RSS is the protocol to query and retrieve updated articles. The reader can be anything you like.
Personally I use rss2email for retrieval and my UI is my email app.