Can you suggest any audio recorder that works well?

My specific need at this moment is to record voice-over audio files which I will add to videos which I'll edit in Kdenlive.

I would recommend Ardour. After years of working with audio editing on GnuLinux I recommend going straight to the best and not wasting time on the "easy" software. Unless you are absolutely sure you will never progress into anything beyond the most basic task. Even then, for basic stuff Ardour is simple enough.

Depending on what your doing it may be easiest to edit audio in the video editing software. There is a plugin to Ardour called xjadeo but it is not a video editor. It is used for playing your final video edit in ardour so you can professionally edit the audio tracks and then combine the two when your done. Probably best for sound tracks but voice tracks with many video edits could be challenging using this method.

Its also really nice to have a simple field recorder. The Zoom H2 is what I have. Its perfect as long as you buy a hairy windscreen for it. I got mine from some guy in Hawaii who makes them by hand.

This will install ardour along with some plugins that you may find useful some day.

sudo apt-get install ardour qjackctl xjadeo calf-plugins tap-plugins swh-lv2 so-synth-lv2 fil-plugins amb-plugins cmt rubberband-ladspa swh-plugins zam-plugins

Hope that helps.