Hi mevla,
The Launchpad type of interface looks intriguing. It might be useful although I have no idea what are the practical principles of what can be done with this, and especially regarding Renoise and Duplex mlrx. So I installed Duplex and start mlrx. Have no Launchpad yet. Looks like it is possible to use mlrx w/o a Launchpad - is it at all ?
If you are using the on-screen version, you might as well go with the monome128 version instead, it’s got a resolution of 16 (double that of the Launchpads).
It might be useful although I have no idea what are the practical principles of what can be done with this
Mlrx is a continuation of a specific type of sequencer called mlr. Unlike a step sequencer, you are playing/sequencing loops on the fly. Each button gives you access to a particular point in time (sample, slice or line offset).
Although mlr has traditionally been all about (ab)using sampled loops, this version works with Renoise phrases too.
I mostly did mlrx for personal use and have no immediate plans of writing a manual for it, sorry.
However, if you have any concrete questions regarding the “Quickstart” located here, feel free to ask 
Any link to any beginner’s demo (many demos on youtube but they do not really show in detail how to use this, and most are not with Renoise) and documentation ? - thanks.
I guess you stumbled upon some of the great mlr videos out there? I would esp. recommend to check out Daedelus, that guy is doing amazing stuff with just a few sounds. I’m not aware of any videos specific tomlrx though.