https://www.mobileread.com/forums/sho...d.php?t=226456
The chance of "Bricking" your device installing these additional programs is very small, as very little of the original software is touched at all. In fact all these programs are launched from a working device running its normal software.
Both CoolReader and Koreader use File Managers. Both are able to see "Hidden" folders so you can hide your ebooks from the Kobo software's processing (often the source of problems, and can be very time consuming). You can build your file structure in any way you wish.
Sergey's Coolreader port has user configurable tap zones and you can define actions for long tap, double tap, ect... Giorgio's Koreader port defaults to right side tap for page forward and uses swipes as well.
You need to get to know any of the readers before you can establish which you like better. None of the additional readers come with any real manual or documentation and there is not that much for the features of the Kobo software. Most of the discussion of the alternative readers takes place here in the "Kobo Developer's Corner". There are a number of us here who will answer any questions you may develop.
Luck;
Ken